Cleavage in a mineral is the tendency for the crystal to split along definite crystallographic planes as exemplified by the rhombohedron cleaved from a calcite crystal shown in Figure 1[Ref1]. These planes of weakness are present within a regular repeating array of atoms and ions within the crystal and are always parallel to a potential face of the crystal. The weakness arises from the chemical bonds between cleavage planes being fewer in number or weaker than those between ions and atoms within the cleavage planes. Accordingly the crystal will tend to split between the cleavage planes and along a plane of relative weakness. When present, it is the uniqueness of the mode of cleavage in a mineral that makes it a tool in its identification.
Mineral crystals exhibit modes of cleavage along six families of planes as shown in Figure 1. Identification of the mode of cleavage and descriptions of its appearance and ease of cleaving can be used as steps in the use of Mineral Identification Keys and data compendiums as listed in References 2-7
The excellent YouTube video of Reference 2 shows how to experimentally develop and evaluate modes of cleavage, parting, and fracture in crystals in their identification. Note that use of eye protective wear is a must while performing these experiments.
Figure 1. Cleavage rhombohedron from a calcite crystal from Naica, Chihuahua, Mexico[Ref9].Figure 1. Six families of cleavage planes exhibited by minerals[Ref10]
As demonstrations of the effects on cleavage of the density and strength of chemical bonds crossing the cleavage plane compared to the cleavage plane itself, consider its behavior in the mica family of minerals, in calcite, and in the diamond.
Cleavage in Muscovite Mica
Muscovite of the mica family, as the other members, only cleaves along planes parallel to the basal plane[Ref11] of a crystal with resulting thin sheets as shown in Figure 2. The structural relationship of the cleavage plane to the relative strengths of chemical bonds between the atoms in the lattice of the muscovite crystal is shown in Figure 3.
Figure 2. Sheets of muscovite mica parallel to the basal crystal plane[Ref12].Figure 3. The basal plane of the muscovite crystal is parallel to the layers of potassium ions (blue) and to the intervening layers of silicon and aluminum atoms covalently bonded to oxygen atoms to form layers[Ref13]. The strengths of these covalent bonds are greatly stronger than the electrostatic attraction between the positive charges of potassium ions and the negative charges of the hydroxyl ions OH2—on the surfaces of the layers; thus, cleavage occurs between the covalently bonded sheets, not through them.
Cleavage in Calcite
Calcite crystallizes in the trigonal crystal system[Ref15] and cleaves along six planes into rhombohedrons as shown in Figure 4.
Figure 4. Rhombohedrons with shiny flat cleaved surfaces as cleaved from a calcite crystal[Ref15].Figure 5. Calcite cleavage rhombohedrons and lattice structure of calcite showing the relative arrangement of the calcium ions Ca2+ and carbonate ions CO32_[Ref9] .
The angles between the legs of the rhombohedral faces are 78.5° and 101.5°.[Ref16] Note that the six cleavage planes lie between extended chain-like arrays of calcium ions and of carbonate ions, and minimal density of bonds crossing the cleavage planes.
Cleavage in Diamond
Cleavage in a diamond crystal can proceed any on of eight octahedral planes which parallel the octahedral faces of a diamond crystal as shown in Figures 6-9. The video shown in Reference 17 demonstrates cleaving of a diamond crystal and the relationship the cleavage plane to the density of bonds crossing the plane.
Figure 6. The basic cubic lattice structure of the diamond crystal with the diagonal octahedral plane is shown in blue[Ref18].Figure 7. View of the diamond crystal lattice showing planes with fewer bonds crossing it lying between two parallel octahedral planes, each with larger densities of atoms and bonds than the plane between them[Ref19].Figure 8. View of the diamond crystal showing that cleavage occurs between the octahedral planes[Ref19].
The parallelism of both a cleavage plane and octahedral faces of a diamond crystal is shown in Figure 9. A representative perfect cleaved surface of a diamond crystal is shown in Figure 10. The white linear features are presne on the outer surface of the cleaved crystal.
Figure 9. Octahedral diamond crystal with cleavage along a plane parallel to two of Its octahedral faces[Ref20].Figure 10. Smooth and shiny cleavage surface of Diamond[Ref20].
Descriptors of Cleavage for Use With Mineral Identification
In Mineral Identification Flow Charts [Ref3] and Mineral Data Tables[Ref4,5,6] not only the mode of cleavage, but descriptions of the quality and ease of cleavage for each mineral also are used as part of the body of information used in identification.
Descriptors of the quality of cleavage are summarized in the table in Figure 11. In addition the difficulty in achieving is described as easy, hard, and difficult to produce[Ref3].
Figure 11. Descriptions of cleavage used in mineral identification[Ref].
Fracture in mineralogy is the texture and shape of the surface formed when the mineral is fractured. Fracture differs from cleavage and parting, which involve clean splitting along a plane surface, as it produces rough irregular surfaces [Ref1]. The appearance of fracture surfaces among minerals is highly varied and is a useful tool in identification. In this part of my Blog I’ll describe the fracture surfaces broadly seen in minerals.
Conchoidal fracture is characterized by smoothly curving nested arcs as those on a seashell[Ref2].
Figure 1. Conchoidal fracture in rose quartz[Ref3,4].
Earthy fracture results in dull, clay-like surfaces without crystalline appearance[Ref2].
Figure 2. Earthy fracture in massive limonite[Ref5,6].
Fibrous fracture is typified by elongated crystal forms[Ref2].
Figure 3. Fibrous fracture in chrysotile (asbestos) [Re7,8].
Granular fracture is produced in aggregates of crystals[Ref2].
Figure 4. Granular fracture in an aggregate of arsenopyrite crystals[Ref9,10]
Hackly fracture produces torn edges and surfaces[Ref2].
Figure 5. Hackly fracture in copper producing torn edges[Ref11,12].
Irregular fracture presents an irregular fracture pattern[Ref2]
Figure 6. Plagioclase feldspar showing an irregular fracture surface[Ref13,14].
Splintery fracture produces thin long cleavages or partings[Ref 2].
Figure 7. Splintery fracture in actinolite [Ref15,16].
Uneven fracture features flat surfaces in a random pattern[Ref2].
Figure 8. Flat surfaces unevenly arrayed on blue sodalite[Ref17,18].
To the great advantage of the beauty of their art, Chinese carvers of jade were guided by themes and decorative motifs in the shaping of their carvings and the choices of decorative motifs adorning them[Ref1-7].
In the Neolithic Era of China ritual jade carvings found in burials reflecting the cosmology of the heavens and the social status of the buried person appeared. The bi disc appeared circa 3400 BC and the cong appearing circa 3300 BC were complementary to each other[Ref8,9]. The circular bi disc with a hole at its center as shown in Figure 1 represented the heavens and the cong with its square cross section with a hole at its center as shown in Figure 2 represented the earth below appeared. Jade carvings of burial objects which reflected attributes of social status, such as authority and power such as the beautiful blade shown in Figure 3 and the coiled dragon amulet shown in Figure 4 appeared in the late Neolithic era
Themes and design motifs from the philosophies of Taoism beginning in the 3rd-4th Centuries BC[Ref10] and Confucianism beginning within the time span of 551-479 BC[Ref11], the Buddhist Religion from the 1st Century AD[Ref12], and mythology with a timeline spanning from 36,0000 years before The Creation to 2852 BC[Ref13] have been lasting influences in jade and jadeite carving into the present day
Taoism embraces nature in its emphasizing the coexistence and harmony between humanity and nature[Ref14]. These relationships can be seen in the jade mountain carvings featuring notable men, such as scholars or leaders of society or of villagers in forest settings as shown in Figures 5 and 6 Appreciation of nature in Taoism also appears in the rich symbology accorded to both animal and plant forms adorning carved jade art objects as shown and described in Figures 7-10.
The innate respect accorded to men of learning and leaders of the royal court and of society in Confucianism[Ref15] may also have influenced the symbology of jade mountain carvings and statues of court functionaries as shown in Figures 11-15.
Four categories of images of different levels of beings in Buddhist cosmology are found in Chinese jade carvings: images of The Buddha, images of Bodhisattvas, images of deities, spirits, heavenly beings, kings of wisdom, and guardian god that serve as protectors of Buddhism[Ref17]. Carved images of The Buddha and other deities are shown and described in Figures 16-22.
Themes from Chinese mythology have been richly incorporated in jade carvings. Carvings of historical humans, animals, plants, and places from Chinese mythology are shown and described in Figures 23-29.
Neolithic Ritual and Ornamental Jade Carvings
Figure 1. Late Neolithic Bi disc carved from nephrite jade, Liangshu culture circa 3300-2400 BC[Ref18].Figure 2. Late Neolithic cong carved from nephrite jade Liangzhu culture circa 2200 BC[Ref19].Figure 3. Ritualistic Chinese jade blade, Neolithic Longshan culture (2900 Bc to 2100 BC)[Ref 20,21]Figure 4. Neolithic carved jade dragon amulet, Neolithicc[Ref22]
Jade and Jadeite Carvings with Taoist Themes and Motifs
Figure 5. Carved jade mountain depicting gathering of scholar-officials composing poetry at Lanting, the Orchid Pavilion[Ref23]. Carvings of mountains embody respect for nature and the desire to find refuge in tranquility[Ref14]. The presence of scholars reflects the respect for them embodied in Confucianism[Ref23,24,25].Figure 6. Carved jade mountain with villagers working in the field with poem by Emperor Quinlong praising village farmers[Ref27].Figure 7. Carved jade tree with birds[Ref28].Figure 8. Carved jade deer which are symbols of wealth and long life[Ref29,30].Figure 9. Carved jade vase decorated with a Zingzhi mushroom which a symbol of long life[Ref30,31].Figure 10. Carved jadeite peach with monkeys; the peach is a symbol of both Longevity and springtime, where somewhat ironically the monkey can symbolize trickery[Ref]30,32.
Jade Carvings with Confuscian Themes and Motifs
Figure 11. Carved jade mountain with Confucius and student[Ref33]Figure 12. Statue of General Kwan Guan carved from white jade[Ref34,35].Figure 13. Carved mossy jade statues of male and female court officials[Ref36,37].Figure 14. Decoration on Royal Seal of the Chinese Emperor Quinlong. 18th Century AD[Ref38].Figure 15. Printing surface of Royal Seal of the Chinese emperor Quinlong, 18th Century AD[Ref38].Figure 16. Chinese carved jadeite statue of The Buddha, Qing Dynasty, 1644-1912 AD[Ref39,40]Figure 17. Jade statue of reclining Chinese Emperor Shouhao[Ref41,42].Figure 18. Celadon jade statue with pearls of the Buddha Shakyamuni, the founder of Buddhism, Quinlong Period (1736-1795)[Ref43,44].Figure 19. Chinese carved jade statue of the Maitreya Buddha (Happy Buddha)[Ref45.46].Figure 20. Chines carved white jade statue of Vidyaraja a Wisdom King and deity in Buddhism[Ref47.48].Figure 21. Jadeite statue of the Bodhisattva Guan Yin, the Goddess of Compassion [Ref49,50].Figure 22. Jade carving of a lotus blossom, the flower of Buddhism[Ref51,52].
Jade and Jadeite Carvings with Themes and Motifs from Chinese Mythology
Figure 23. Celadon jade statue of a recumbent Qilin (Dragon Chimera)[Ref53,54].Figure 24. Chinese grey-green and russet jade mountain with Pangu, the Creator of earth, holding a shovel and emerging a cave with whorls of smoke and a dragon beneath[Ref55,56].Figure 25. Chinese yellow jade carving of monkey[Ref57].Figure 26. Nephrite jade carving of a Rui Shi (Guardian Lion, Foo Dog)[Ref58,59].Figure 27. Carved jade mountain with Yu the Great subduing the Great Flood with hammers, axes, and levers by redirecting the flow of water[Ref60,61].Figure 28. Chinese jade carving of a Fenghuang (Phoenix) with lotus flower[Ref62.63.Figure 29. Jade carving of Nuwa, the mother goddess of Chinese mythology, repairing the sky[Ref64,65].
From the late Neolithic Age (circa 3500 BC-2070 BC) into today the crafting of jade art objects in China has produced beautiful and magnificent art objects which exhibit remarkable diversity of both color and form as shown by the carved nephrite jade pendant with phoenix pattern and the funerary Bi Disc with rain pattern in Figure 1[Ref1]. In this blog I’ll describe the tools and techniques with their technological advances and show corresponding art objects of increasing complexities of design and execution.
As shown in Table 2 of Reference 1 as presented in Figure 1 below, shaping techniques, such as cutting, grinding, carving, drilling, piercing, carving to egg shell thinness, and polishing began in the Neolithic Age (approximately 10,000 BC-3000 BC[Ref2] and are still practiced today, with the benefit of improved technologies which have evolved over time.
The authors of Reference 2 propose the evolution of jade rotary carving tools to have proceeded over five generations as described in the text and summarized in Table 2 of the Reference.
Figure 1. Carved nephrite jade amulet with phoenix pattern and funerary Bi disc with grain pattern; Han Dynasty, ~275-141 BC[Ref1].Table 1. Table reviewing the advance of jade shaping tools and craftsmanship[Ref2]
First Generation Advances in Jade Carving, ~3500 BC – ~2070 BC[Ref2].
In the First Generation a primitive rotary jade carving machine first appeared in Neolithic Longshan[Ref2,3,4] and Liangjiatan (Liangzhu[Ref5]) cultural sites and featured tools surfaced with natural materials such as stone wood, and bone. Major features of the primitive carving machine allowed the operator to be seated and the fixed shaft of the tool to be manually rotated, both probably lending better control than that obtainable with hand held tools.
The cong shown in Figure 2, is a ritual vessel used in burials[Ref6]. It is an exceptional example of a nephrite jade object carved during the era of the Liangzhu Culture. The use of the surfaces and shaped edges of rotating grinding tools such as discs with abrasives in shaping and polishing of the structural features of the cong seems evident. Also the use of a rotating hollow tube with an abrasive in generating the eye features of the masks at the corners of the cong is evident . Use of the surfaces of small wheels with abrasives to generate relief curves such as those on edges and eyebrows of the mask also seems evident.
Second Generation Advances in Jade Carving ,~2070 BC- ~ 6 AD[Ref2]
Use of a bronze rotary machine began during the Xia and Shang Dynasties, 2700-1046 BC was in use to the early to mid-Chunqiu Period, 9~620 BC[Ref8,9.10]. Operators may have been kneeling and able to obtain higher rotational speed through the forward thrusting of both the upper body and arm rather than the use of the arm of seated person. Continued use of grinding tools with symmetric rotating forms is evidenced in the carved human face shown in Figure 3.
Figure 3. Carved jade human face ornament, Shang Dynasty (1600-1046 BC)[Ref11].
Third Generation Advances in Jade Carving, ~6th Century BC– ~581 AD[Ref2]
The manually driven iron rotary machine first appeared over the Chunqiu Period until the Nan-bei Dynasty, 770-589 BC[Ref10,12]. Operators still kneeled when using the machine. The newly developed iron grinding tools were sharper and maintained their sharpness and shapes longer than bronze tools. Finer detailed carving could be realized as shown by the carved jade sword sheath in figure . Use of iron tools enabled the appearance of Han badao carving in which deep narrow cuts were used to define the shape of carved objects such as the pigs shown in Figure 4. Burial suits in which small plates of jade are stitched together with metal wire as shown in Figure 6 appeared in the Han Dynasty (206 BC – 8 AD).
Figure 4. Pair of jade pigs carved in the Han badao style, Western Han dynasty 9206 BC-8 AD [Ref13]. They seem to present a modern appearance.Figure 5. Carved jade sword sheath with bird and dragon decorations[Ref14]. Not the fineness of the carved detail.Figure 6. Jade burial suit sewn with gold wire, Han Dynasty (206 BC-8 AD)[Ref15].
Fourth Generation Advances In Jade Carving, ~581-AD-1960 AD[Ref2]
The treadle-driven table-type iron rotary machine as shown in Figures – and – with tools as those in Figure – has been used from the Sui and Tang Dynasties, 581-618 AD and 618-907 AD[Ref 16,17] into the 1950s. the switch in seating followed the availability of indoor furniture. The use of the foot-driven treadle freed both hands for manipulation with finer control of the jade object during carving as evidenced by the carved lady and horse, respectively in Figures 7 and 8.
Figure 7. Carved jade flying lady, Tang Dynasty (618-907 AD)[Ref18].Figure 8. Carved jade horse, Tang Dynasty, 618-907 AD[Ref19]Figure 9. A restoration of a fourth-generation table-type iron Rotary machine[Ref2].Figure 10. A fourth-generation iron rotary carving machine[Ref20]. Figure 11. Rotary tools used in treadle-driven rotary machine of Figure–[Ref20].
Fifth Generation Advances in Jade Carving,1960-Present[Ref2]
The modern rotary carving machine was first introduced in the 1960s and now takes the forms of a fixed or hand-held precision tool on a flexible shaft and a computer-controlled precision machine with motion in three mutually perpendicular directions and three mutually perpendicular rotary tools for carving complex 3-D shapes. Additionally the emergence of synthetic diamond and carborundum (silicon carbide) abrasives and polishing agents have enabled better tool performance. With the increased precision of tools a number of carving techniques flourished. Use of a modern rotary tool is shown in Figure 12 and a computer controlled machine in Figure 13.
Carved objects became more elaborate post 1960. Qiaose carving in which the carved form capitalizes on regions of color variation in the jade to enhance the aesthetics of the object, such as the carved jade Chinese cabbage shown in Figure was better enabled[Ref]. New precision rotary machines could be used to carve vessels with egg-shell thin walls and forms of egg-shel thickness as shown in Figures 15,16 and17. Use of the computer-controlled machine enabled carving of more complex patterns for inlay of gems in jade objects such as the Quing Dynasty white nephrite egg-shell bowl of Islamic style, 2010 shown in Figure [Ref2].
Figure 12. The head of the rotating tool can be fixed and used as shown in the upper-left and lower-left panels with the object controlled by both hands of the operator or With use of the flexible shaft used withboth the position of the tool and object changeable as shown in the lower-right panel. Multishaped tools are shown in the panel on the upper right[Ref2].Figure 13. Computer-controlled engraving and shaping machine. The jade piece is held on the table which can move in two mutually perpendicular directions as well as up and down. With the machine a jade object which would require 20 days to carve manually can be made in three to four days[Ref2].Figure 14. Carved jadeite Chinese cabbage, Quing Dynasty, 1889 AD[Ref21]Figure 15. Egg-shell thin nephrite jade vase with an even, thin (~0.1 cm) wall and small scale intricate surface relief carved with use of a computer-controlled machine, 2015[Ref2]. The vase measures ~ 34.6 x 11.0 cm.Figure 16. Nephrite jade egg-shell carving titled “To Mountain” symbolizing “diligence” as the path to the mountain of knowledge”[Ref2]. The wall segments taper from 2.53 to 0.085 cm.Figure 17. Islamic jade egg-shell bowl of white nephrite jade inlaid with gems and gold, Quing Dynasty, 1644-1911 AD[Ref2]. Numerous jade art objects made in China reached India during the Mughal Era[Ref 21,22].
Since ancient times jade[Ref1] has been used by artisans to create beautiful jewelry and works of art. Art objects of jade have been carved in China for more than 6000 years[Ref2] as exemplified by the jade dragon carved during the Zhou Dynasty (5th – 4th century BC) as shown in Figure 1. In Central America, the Mesoamerican cultures, the Olmecs, Mayans, and Aztecs[Ref3,4,5,6] prized jade for jewelry and religious objects as evidenced by the art objects in Figures 2-4. Since the arrival of the ancestors of the Maori in New Zealand in the 13th century[Ref7] jade, also called greenstone, or pounamu in the Maori language, has been imbued with spiritual significance and used to fabricate beautiful jewelry and objects such as shown in Figures 5-7[Ref8].
In this Blog I’ll describe those properties of the color and toughness of jade that underlie its long use as a gemstone in creating jewelry and artworks. I’ll also describe the current global sources of rough jade and jadeite and their geological origins. Also, in two subsequent Blogs I will describe first the long history jade as a gemstone, and present second a Gallery of jewelry and art works from around the ancient world.
Figure 1. Jade carving of a dragon, Zhou Dynasty[Ref9].Figure 2. Carved jade Olmec mask, Mexico, 900-400 BC(Ref10].Figure 3. Mayan jade funeral mask and jewelry of the Mayan king of Palenque, K’inich Tanaab’ Pakal . 603-683 AD[Ref11,12].Figure 4. Caved jade statue of the Aztec rain god Tlaloc, Central Mexico, 13th – 16th Century[Ref13].Figure 5. Maori style jade modern carving of a fishhook (Matau)[Ref 14,15].Figure 6. Jade carving of a human figure, an Hei tiki which represents the first man in Maori myth, 1700-1847Ref14,16].Figure 7. A jade (greenstone) hand club, a gift to the Duke of Windsor, April-May 1920[Ref14,17].Figure 8. Nephrite jade Maori carving of a spiral (koru) [Ref18].
JADE AS A GEMSTONE
Jade is a cultural term that encompasses a very durable silicate rock material which has been used in tool-making, sculpture, and jewelry, and other objects for over 5,000 years[Ref9]. Jade as a gemstone encompasses two rock types nephrite and jadetitite, the latter primarily comprised of the mineral jadeite[Ref1]. The amphiboles of the tremolite-actinolite series of minerals are the major components of nephrite jade. Mineral compositions of nephrite and Fen Sui Jadeite are described in Table I.
TABLE I. THE MINERAL COMPOSITIONS OF NEPHRITE AND FEN SUI JADEITE
NEPHRITE [Ref19,20]
JADEITITE [Ref21,22,23,24,25]
Major Minerals
Major Minerals
Felted amphiboles of the tremolite-actinolite series
Jadeite-Kosmochlor mineral series, which are pyroxenes
A number of the properties of jade underlie its wide use as a gemstone. Its many rich colors and its soft luster underlie its wide aesthetic use in jewelry and art objects. Its hardness and toughness allow its use in forms of jewelry susceptible to wear. In this section I’ll describe the sources of the various colors of nephrite and jadeite jades, and describe its physical properties underlying its use in its durable jewelry.
Sources of colors in nephrite jade
Absorption of visible light by iron, chromium, and manganese ions present in the members of the Tremolite-Amphibole mineral series which comprise nephrite jade underlies its colors. Results of a study to determine the identity of these metal ions that was made on over a broad sampling of colored nephrites from China have determined the color-metal-source relationships shown in Table 4 of Reference – as presented in Figure – below. The visible light absorption spectra of the colored specimens are shown in Figure 7 of the reference.
Figure 9. Metals and mechanisms responsible for the colors of nephrite jade[Ref].
Among the mechanisms the electron (charge) transfer responsible for colors, elevation to a higher energy d-orbital of a transition metal ion and decay back to the ground level such as indicated by the excitation of an impurity manganese ion,
Mn3+ (4Eg)-> 5T2g and by the excitation and decay of a constituent iron ion, chromium ion Cr3+ (4A2) ->4T2,, or iron ion Fe3+ ( 6A1) -> 4E + 4A1(4G). Also electron (charge) transfer from an ion richer in electrons to one less rich such as between oxygen and iron ions O2- -> Fe3+, between iron ions Fe2+ -> Fe3+, and between iron and titanium ions Fe2+ -> Ti4+ can contribute absorption peaks to the absorption spectrum of nephrite jade. Annotated absorption spectra of nephrite jade specimens of various colors shown in Figure — of Reference– illustrate the relationship between absorption peaks and transmission windows within each spectrum[Ref25]..
Micron-sized iron oxide mineral impurities listed in TABLE – also can lend colors to nephrite jade, and also contribute to the yellow to black range of colors in jadeite.
TABLE II. IMPURITY MINERALS CONTRIBUTING TO YELL0W-BLACK COLOR RANGE IN NEPHRITE[Ref1]
COLOR
MINERAL
FORMULA
Yellow
Limonite
FeO(OH) – nH2O, n is arbitrary
Red
Hematite
Fe2O3
Black
Magnetite
Fe3O4
Black
Chromite
FeCr2O4
Brown
Combinations of Limonite, Hematite, and Magnetite
As above
Sources of colors in jadeite
Iron, chromium, manganese, and silicon ions in the lattice of jadeite (NaAlSi2O6) are responsible for its green blue, and lavender colors as summarized in TABLE –[Ref1]. In jadeite with hues of green both the ferric Fe3+, chromicCr3+ ions substitute for aluminum ion Al3+. In blue and lavender jadeite ferrous, and ferric ion, Fe2+ and Fe3+, and the manganese III ions Mn3+ substitute for aluminum ions. The titanium ions Ti4+ substitute for the Silicon ion Si4.
Light absorption by the ferric ions in jadeite produces a peak in the blue at 437 nm and absorption by chromic ions results in peaks at in the 580-700 nm range[Ref1].
In blue and violet jadeite absorption of light by a ferrous ion which results in transfer an electrons through an oxygen site to a neighboring titanium ion (charge transfer) results in a wide absorption peak at 630 nm[Ref1,3].
Micron-sized iron oxide mineral impurities listed in TABLE – can lend colors to nephrite jade, and also can contribute to the yellow to black range of colors in jadeite.
TABLE III. TRANSITION METAL ION SOURCES OF COLOR IN NEPHRTE JADEITE
COLOR
ELEMENT
ABSORPTION CENTER
REFERENCE
Green
Iron and Chromium
Cr3+, Fe3+
Figure 9 in Ref 28.
Greyish Green
Iron
Fe3+
Figure 13C in Ref 28.
Blue
Iron and Titanium
Fe3+, *Fe2+ -O- Ti4+
Figure 12 in Ref 28.
Lavender (violet)
Iron, Manganese, and Titanium
Fe3+, Mn3+, *Fe2+-O-Ti4+
Figure 13D in Ref 28.
Lavender (Purple)
Iron and Manganese
Fe3+, Mn3+
Figure 13B in Ref 28.
Yellow, Brown, Red, Black
Iron, Oxygen, and Hydrogen
Fe2+, Fe3+, O2-, OH1-
29
*Charge transfer complex[Ref3]
Figure 10. Neolithic nephrite axe from the Chinese Lingshu Culture, approximately 3300-2220 BC[Ref]32,33.]
Strength properties of jade
The hardness of a material is its ability to resist abrasion; the toughness of a material is its ability absorb energy and plastically deform without fracturing under stress[Ref31]. These features underlie the use of nephrite in ancient times in fabricating durable tools such as the axe shown in Figure 10 of fabricated in China during the era of the Liangshu Culture in approximately 3300-2220 BC.The range of Mohs Hardness values of nephrite jade lie in the range of 6.0-6.5[Ref], and are less than those of jadeite, which lie in the range 6.5-7.0[Ref]. The hardness of both lie just below that of 7.0 for quartz[Ref].
In the 1973 study of Bradt, Newnham, and Biggers values of the fracture toughness and fracture strength of both nephrite and jadeite jade were determined with their measured values interpreted in terms of their microcrystalline structures[Ref38]. Comparison of the values of these quantities for both varieties of jade and with the values of fracture toughness for both quartz and corundum, both well-known as gemstones, are presented in TABLE .
TABLE IV. STRENGTH AND TOUGHNESS OF JADE AND OTHER GEMSTONES
GEMSTONE
FRACTURE STRENGTH Dynes/cm-2
FRACTURE SURFACE ENERGY Ergs/cm2
FRACTURE TOUGHNESS Dynes/ cm-(3/2)
Nephrite
2.22 x 109
2.26 x 105
7. 7 x 108
Jadeite
1.02 x 109
1.21 x 105
7.1 x 108
Quartzite
—–
4.32 x 103
7 x 107
Alumina(Polycrystalline aluminum oxide, corundum)
—–
1.5—5.0 x 105
3.5-4.4 x 108
Quartz Crystal
—–
1.03 x 103
5.0 x 107
Corundum Crystal
—–
6.0 x 10 2
7.0 x 107
Examination of the TABLE IV shows the values of fracture strength, fracture free energy, and fracture toughness of nephrite and jadeite to exceed those of alumina and quartzite, both also being polycrystalline materials, and far exceed those of single crystals of quartz and corundum, both also known to be durable gemstones.
The results show that propagation of cracks across crystals and along boundaries between crystals require considerably more energy than propagation along cleavage and parting planes in crystals. Propagation of cracks across and between crystals of jadeite and crack propagation along boundaries between elongated crystal grains and bundles of grains in nephrite are shown in Figures -,-,-. Both fibrous structure and trans-granular fracture impede crack propagation and toughen the material.
Figure 11. Nephrite and jadeite microstructure[Ref38].Figure 12. Fracture surfaces of jadeite showing trans-granular [Ref38].fracture.Figure 13. Fibrous fracture surfaces of nephrite with interlocking amphibole crystals[Ref38].
Geology and Occurrences of Nephrite and Jadeitite
Both nephrite jade and jadeitite jade are found world wide as shown in the map of Figure 14.
Figure 14. Sources of nephrite jade and jadeite are distributed worldwide[Ref39].
Among known world-wide sites of jade production, the main sources of nephrite production are in the United States and British Columbia[Ref39,40]; the main sources of Jadeite are in Myanmar, Russia, Central America, and Japan[Ref40].
Examples of jadeite rough and nephrite rough materials from current sources are shown in Figures 15 and 16.
Figure 15. Boulder of jadeite rough from Myanmar[Ref]. Figure 16. Boulder of Canadian nephrite jade[Ref].
The sources of both jadeite (jadeitite) and nephrite as shown in the map of Figure 14 are located along the boundaries of colliding tectonic plates comprising the earths lithosphere which underlie the continents and ocean beds and meet at boundaries at which the continental plates override the oceanic plates as shown in Figure 14[Ref39,43].
Geological processes in formation of jadeite
The geological processes of the formation of jadeite are summarized below in Figures 17-19.
Figure 17. The crust of the oceanic plate undergoes subduction underneath the crust of the continental plate[Ref44].Figure 18. The sinking oceanic plate drags fragments of the sedimentary rocks of the continental plate[Ref44].Figure 19. At lower depths chemical reactions in fluids released dissolved metal salts and silicates which crystallized into jadeite at pressures in the range 87,000 507,500psi and 250-600° C at depths of 20-129 km[Ref44]. Subsequent geological processes exposed the rocks containing the jadeite.
Geological processes in formation of nephrite jade
Most nephrite occurs along fault contacts between serpentinite [Ref46] and in basic to acidic igneous rocks or sandstone following obduction[Ref47] of the serpentinite body by the oceanic plate. It forms by the action of calcium- and silica-rich fluids on the serpentinite with the nephrite replacing the serpentinite. under low pressure-temperature conditions[Ref48].
Nephrite can also from in dolomitic marble from calcium- and silica-rich solutions from intruding molten magma of granite composition[Ref49].
In this Blog I’ll describe how biomaterials including animal and plant fossils are included and preserved in amber formed from tree resin, which by its stickiness can entrap objects which contact its surface as shown in Figure . With further addition of the resin the object is sealed within the resin and out of the surrounding biotic environment. With the passing of geological time amber forms from the resin and encloses the organism as described in the legend of Figure 1-[Ref1,2].
Figure 1. Taphonomy (Process of the formation) of amber with preserved organisms[Ref16].
In the environment external to the tree in which the amber forms, oxidation and temperature extremes and biotic factors such as bacteria and scavengers accelerate decomposition of an organism; instead the environment within the tree resin capturing the organism provides protection against the biotic environment, allowing the preservation processes to proceed to fossilization. Following entrapment of the organism within the resin, the continuing loss of volatile oils called olio-resins from the resin, which continues through evaporation, coupled with polymerization reactions of terpenoids to form a large network of molecules and other organic compounds result in the formation of amber with time. Under conditions that are not extreme, the amber is impervious to the outside environment and shields the fossilized material during its preservation. Studies of factors affecting preservation have shown that the type of tree resin, hence its chemistry and possible chemical attack on the material, the degree of dehydration, and activity of gut microorganisms are some major factors affecting the preservation of soft tissues of organisms[Ref16,17].
Gallery of Some Fossils Preserved in Amber
Some of the most extraordinary discovered fossils range from insects to plants and animals preserved in amber. —“[Ref3]. To illustrate, a Gallery of some unusual, and representative preserved fossils which I found very interesting are shown beautifully in the following figures.
Figure 2. Lyme Disease spirochete-like bacteria (Borrelia burgdorferi)are present in a tick preserved in15-20 million-year-old Dominican amber[Ref4]. The bacteria are present as the approximately 1-mm sized brown-black spheres located between the juncture of the legs and the body of the tick.Figure 3. The flea Atopopsyllus cionus, a genus entirely new to science, is preserved in 20 million-year-old Dominican amber[Ref5]. The brown-colored rod-like and spherical bacteria seen within the flea are similar to the bubonic plague bacteria (Yersinia pestis). This fossil specimen may show an early connection between insects and pathogenic microorganisms.Figure 4. A millipede preserved in 99 million-year-old Burmese amber differed in appearance from those of the order existing today, Callipodia, and was called Burmanopetallum inexpectatum[Ref6].Figure 5. A baby salamander of the extinct species Palaeoplethodon hispaniolae preserved in 20 million year-old Dominican amber[Ref7]. The fossil revealed that salamanders once lived on an island in the Caribbean Sea where they are now absent. The lack of a forelimb reveals attack by predator before entrapment in the parent resin with following containment in amber.Figure 6. Tufted tube-likeand protofeathers of a dinosaur preserved in 78-79 million-year-old Canadia amber{Ref8,9,10]Figure 7. A 47.5 millimeter-long baby snake preserved in 99 million-year-old Cretaceous amber found in Myanmar[Ref11]. Its taxonomy is connected to snakes from Argentina, India, and India.
Figure 8. Mammalian hair preserved in amber which 100 million years ago In the Cretaceous in Era and found at Charentes, France[Ref12,13]. With the scale bar in Panel “a” being 100 μm length the diameter of the hair is seen vary between 32 and 48 μm and the hair to be ~ 2.4 mm in length. In panel “b” the fossil hair is seen to comprise be hollow surrounded with a layer of brown carbonaceous material replacing the cuticle and with irregular shaped grey carbonaceous debris. In Panels “d” and “e” the wavy scale pattern and markings on the cuticle are shown clearly.
Figure 9. Leaves of the carnivorous plant Roridula gorgonias preserved in Eocene Baltic Amber between35 and 47 million years-go and found near Kaliningrad, R.ussia[Ref14]. The venom containing glands project laterally from the surface region of the leaf away from the axis of the plant. Scale bars: A and B; 1mm, C 100μm.Figure 10. Flower of the plant species Strychnos electri preserved between 45 and 15 million years ago in Dominican amber[Ref15]. Being of the Genus Strychnos; the plant may have been poisonous.
Biomaterials Found Preserved in Amber
Preserved biomaterials range from biochemicals to fossilized cells, tissues, and entire organisms. Representative examples of these preserved biomaterials are presented below in TABLES I, II, III, and IV.
None of the structural biomolecules of animal and plant life forms are preserved intact in amber. Instead chemical reactions acting on the chitin within the cuticle of arthropods and within the cell walls of fungi and plants, and on the proteins within feathers, cuticle, and soft tissues of animals, respectively form polysaccharides and amino acids as summarized and referenced in TABLE –. Of pigmented biomolecules red hemeporphyrins and melanin are preserved as seen in the table while carotenoids are not.
Recovery of geologically ancient DNA would be of immense value to biology.
However, according to the paper by Hebsgaard, et al[Ref18], the authenticity of the reports of the presence of DNA being found preserved in amber, References 12,16,17,19,23,24 in the paper, is questionable. As stated in the paper by Hebsgaard et al in Box 2 of their paper, “It is concerning that all claims published to date on DNA surviving over geological time spans have not followed the most fundamental of these authentication criteria.”
Biochemicals which have been found in amber are summarized in TABLE I. Examples of preserved bio-materials ranging from bio-chemicals are described with illustrated references in TABLE I, and from tissues to organisms are described in the text and summarized with illustrated references in TABLE II, and in TABLE & III.
TABLE I . SOME EXAMPLES OF BIOMOLECULES FOUND PRESERVED IN AMBER
BIOMOLECULE
BIOLOGICAL SOURCE
GEOLOGICAL AGE (Million-years-ago)
REFERENCE
N-acetylglucosamine
Fungus Chitin
Cretaceous, 138-66
19, 20
β-1,3 and β- 1,4-linked polysaccharides
Fungus Chitin
Cretaceous, 138-66 Mya
19
Amino Acids
Feather Keratin
Insect Protein
Cretaceous extending into Eocene, 99-44 Tertiary – Creataceous 130-40 Mya
21
22
Melanin
Feather
Eocene, 66-23 Mya
23
Cells and both soft and hard tissues are found preserved in amber as shown in TABLE II.
TABLE II. EXAMPLES OF ANIMAL AND PLANT CELLS AND TISSUES PRESERVED IN AMBER
TISSUE
HOST
GEOLOGICAL AGE
REFERENCE
FIGURE NUMBER
Flight Muscle, fibers and mitochondria
Fly
Miocene 23-5 Mya
24
Figure 2C
Neural, axons & glial cells
Beetle
Oligocene 34-23 Mya
25
Plate1, Figures 5 & 6
Eye, Lens, pigment cells, crystalline cone
Fly
Eocene, 45 Mya
26
Figure 1
Cuticle scales
Cockroach, Beetle, Grass-hopper
Cretaceous, ~130 Mya
27
Figure 8
*Cuticle & soft tissues in sections
Fly
28,29
Blood, Red Blood Cells
Monkey, Tick
Oligocene, 30-15 Mya
30
Three figures
Feathers
Dinosaur
Cretaceous, ~ 105 Mya
31
Three figures
Bone
Lizard
Miocene, ~20 Mya
32
Figures 1, S1 & S2
Cypress Plant
—-
Eocene, ~45 Mya
33
Figures 1 & 2
Fern
—-
Cretaceous. ~98 Mya
34
Figures 1 & 2
Liverwort
—-
Cretacwous ~100Mya
35
Figures 1-10
*Images obtained by micro CT scanning.
Some animals from the Cretaceous Era into the Miocene Era found preserved in amber are presented in TABLE III.
TABLE III. SOME ANIMALS FOUND PRESERVED IN AMBER
PHYLUM/Animal
GEOLOGICAL AGE (MILLION YEARS AGO)
REFERENCE
FIGURE NUMBER IN REFERENCE/ NUMBERS OF FIGURES
MOLLUSCS
Snail
Cretaceous ~99
36
Figures 1-7
Ammonite
Cretaceous ~99
37
Five figures
ARTHROPODS
Fly
Cretaceous 135-65
38
One figure
Beetle
Cretaceous ~100
39
One figure
Bee
Cretaceous ~100
40
Ten figures
Millipede
Cretaceous ~99
41
Two figures
Scorpion
Miocene 23-15
42
Three figures
VERTEBRATES
Salamander
Oligocene 30-20
43
One figure
Lizard
Cretaceous ~99
44
One figure
Snake
Cretaceous ~99
45
One figure
Dinosaur
Cretaceous ~99
46,47
k-one figure., l-one figure
Bird
Cretaceous ~99
48
One figure
MAMMAL
Shrew-like
Cretaceous
49
None
Some plants living from the Cretaceous Era into the Eocene Era found preserved in amber are presented in TAVLE IV.
Amber is a hard resin formed from tree sap by fossilization and is many millions of years old[Ref1]. Since Neolithic times (about 9000-3000 BC) and before the Copper Age[Ref]2) amber has been highly valued as a gemstone and used to create beautiful jewelry and artworks. Wide use of amber in Early Europe and in the area of the Mediterranean Sea is shown in jewelry and artworks displayed in Figures 2-7. Works from the Medieval Era to the present are shown in Figures 8-13.
In this Blog chemical and physical properties of amber which underlie its beauty and use as a gem are described in descriptions of its chemical and mechanical properties, and the sources of its colors. Also preservation of fossils of insects and other organisms in amber is described briefly.
AMBER IN ANCIENT EUROPE
As shown in Figure 1 amber from sites (red) where amber was found in Ancient Europe were distributed widely from their greatest concentrations along the coast of the Baltic Sea and along the North Sea coast along Jutland. As indicated by the routes indicted in black and red movement of amber could proceed from the North and Baltic Seas to Mediterranean countries terminating in what are now Italy and Greece[Ref]. Collateral routes led to the Black Sea, Syria, and Egypt[Ref3]. Amber was moved further Eastward along the Great Silk Road to China and Southeast Asia[Ref4]. Collateral routes between sites of origin over what is now Europe to the major North-South routes served to distribute locally mined amber around the continent.
Figure 1. Amber sources and trade routes in Ancient Europe[Ref3].
AMBER JEWELRY AND ART WORKS FROM ANCIENT TIMES INTO MODERN TIMES
Figure 2.Etruscan pendant, Foreprts of a wild boar, 525-480 BC[Ref5].Figure 3. Italic carving of horse head in profile, 500-400 BC[Ref5].Figure 4. Italic or Etruscan necklace with carved amber scarab beetle and large carnelian beads mounted in gold, 550-=400 BC[Ref4].Figure 5. Greek gold necklace with amber beads mounted in gold. 6th-4th Century BC[Ref5]Figure 7. Amber intaglio finger ring, Egypt, New Kingdom, 1550-712 BC[Ref5].Figure 6. Roman amber amulet carved in shape of gladiator’s helmet, circa 1st-2nd Century AD[Ref6].Figure 7 Roman die carved from amber, 100-200 AD[Ref5]Figure 8. Amber Paternoster, Middel European, circa 1260 AD[Ref7].Figure 9. Amber greyhound pendant, Czecj 1600[Ref8].Figure 10. Amber in gold earrings, Georgian Era, 1714-1830 AD[Ref9].Figure 11. Necklace with amber set in gold, Italian, circa 1860-1870[Ref10].Figure 12. Egyptian Revival amber and opal necklace set in gold, Art Nouveau, 1890-1910[Ref11].Figure13. Art Deco styled amber earrings set in Russian Silver Gold Vermeil, Recent[Ref12].
THE CHEMISTRY OF AMBER
The fossilization of tree sap into amber proceeds by crosslinking of di-terpenoid and tri-terpenoid molecules by free-radical polymerization[Ref13,14]. Over the millions of years during which crosslinking occurs to form polymers; polymerization, and cyclisation also occur resulting in new chemical compounds[Ref13,15,16]. The resulting mixture of substances can be described in terms of its carbon, hydrogen, and oxygen contents by the formula C10H16O. Sulfur comprising up to 1% of chemical species may also be present[Ref].
SOURCES OF THE COLORS OF AMBER
Figure 14. Colors of Baltic amber[Ref17].
AMBER PIGMENTS
Studies[Ref18-27] on specimens of amber gathered from worldwide sources have shown that members of the chemical terpenoid family[Ref13] as well as other chemical species can contribute to the yellow to brown, red, and black colors of amber as shown by specimens of Baltic Amber in Figure 14.
As an example a study conducted on Baltic amber separation by liquid chromatography* showed separation of terpenoids and unsaturated organic compounds showed colors ranging between yellow, shades of red, and brown as shown in Tables I and II [Ref25]. These colors have been found in amber gathered from around the world.
*In separation of chemical species by liquid chromatography[Ref27] specific chemicals are used to sequester other chemical species which transport at different rates during separation by gravity resulting in degrees of separation from their collective position which range between 1.00 and 0.00 as shown by the example in Figure 15 .
Figure 15. Positions of separated chemical compounds in thin film chromatography. The positions of each is unique[Ref27].
AMBER WITH COLOR DUE TO FLUORESCENCE
Some amber from the Dominican Republic exhibits a strong Cobalt Blue fluorescenceas shown in Figure 16[Ref28]; some amber found in the Baltic, the Ukraine, Far-Eastern Russia, and Sumatra also exhibit blue fluorescence[[29,32]. Studies on these ambers have shown that the blue fluorescence in ambers from the Dominican Republic and Sumatra stems from the ring-like organic molecule perylene[Ref28,30,31] and that from the amber from Far-Eastern Russia stems from the pyrene eximer[Ref29,34,35].
Figure 16. Blue-colored amber from the Dominican Republic. The color is due to fluorescence[Ref27].
PHYSICAL PROPERIES OF AMBER
Being an organic resin amber is amorphous with no crystalline structure; accordingly it is not classified as a mineral but as a mineraloid, a mineral-like material[Ref36]. It’s Mohs Hardness is in the range 1-3 and it fractures in brittle fashion but is tough in its tenacity at temperatures near room value.[Ref36]. At
higher temperatures near210°C amber can be bent, allowing repair of amber pipe stems, as well as formed by pressing and sintering pieces together[Ref37.38]. The latter process allows construction of art objects such as a box as shown in Figure 17. [Ref39].
Figure 17. Box constructed of pressed and heated Baltic amber[Ref39].
PALEONTOLOGY OF AMBER
Organisms and organic matter such as a feather can be trapped and ultimately over long time become inclusions in amber. With initial entrapment on the surface of amber and subsequent deposit of more amber organism can be entrapped as shown in the sequence in Figures 18 and 19. A great variety of organisms can be preserved as shown in Figure . Following initial and subsequent deposits of sticky amber and entrapment episodes a volume of amber containing fossils is attained[Ref40].
Figure 18 . Organisms preserved in amber. The legend for this Figure is shown in Figure 19 [Ref40]. Figure 19 . Legend for organisms in Figure 18. {Ref40].
Meteorites are stuff from outer space; each is a solid piece of debris which formed from dust within the protoplanetary disc or from object such as an asteroid, planetesimal, or planet, and which travels through space and falls through the atmosphere to the surface of earth. As alien objects which fall dramatically they have evoked interest and wonder among many people. I remember vividly at the age of ten watching with my dad the meteorites fall during a Perseid Meteor Shower such as shown in time lapse photography in Figure 1. We both were greatly excited by the sights of the darting meteor trails and the awe felt by both of us felt was almost palpable. This fond memory has prompted me to write about meteorites in hopes of further acquainting my readers with them.
I will write three blogs about meteorites; in the first I’ll consider both iron and stony-iron meteorites, and the following blogs will be about chondrites and achondrites, both classes of stony meteorites, and lastly about chondrules, which are constituents of chondrites and are sub-millimeter to millimeter-sized spherules containing silicates and another minerals and are often quite beautiful.
The three major classifications of meteorites based on their mineral compositions are: stony meteorites which are comprised of silicate minerals, iron meteorites which primarily are comprised of an alloy of iron and nickel, and stony-iron meteorites which are comprised of a mixture of iron-nickel alloy and silicate minerals. Iron-nickel meteorites can also contain sulfide, carbide, phosphide minerals of iron, nickel, cobalt, and chromium, as well as native carbon. The class of stony-iron meteorites are comprised of two subclasses, pallasites and mesosiderites[. The distribution of classes of meteorites found world-wide are shown in TABLE 1 and examples of them are Figures 2-5.
Figure 1. Time-lapse photograph showing meteors falling during a Perseid Meteor Shower[
TABLE 1. DISTRIBUTION OF CLASSES OF METEORITES BY FALLS FOUND THROUGHOUT THE WORLD
METEORITE CLASSIFICATION
PERCENTAGE
Stony
97.4
Iron-Nickel
2.0
Pallasite
0.2
Mesosiderite
0.4
IRON AND STONY-IRON METEORITES
Meteorites containing an iron-nickel alloy are classified as the iron meteorites, and the stony iron meteorites, the latter including the pallasites and the mesosiderites.
In the iron meteorites the iron-nickel alloy is present as two minerals: kamacite which contains up to 7.5% dissolved nickel in solution with iron and taenite with more than 25% nickel in solution. Other minerals which contain iron, nickel, cobalt, phosphorous, oxygen, sulfur, and carbon in lesser abundance may be present in iron meteorites. These minerals with their compositions are summarized in Table 2. Each minda.org reference contains representative photographs of the mineral.
TABLE 2. MAJOR MINERALS FOUND IN IRON AND STONY IRON METEORITES
MINERAL
CHEMICAL FORMULA
MINDAT.ORG REFERENCE
Kamacite
(Fe,Ni)
8
Taenite
(Fe,Ni)
9
Troilite
FeS
10
Daubre’elite
Fe2+Cr3+2S4
11
Cohenite
(Fe,Ni,Co)23C6
12
Schreibersite
(Fe,Ni)3P
13
Chromite
Fe2+Cr3+O4
14
Magnetite
Fe3O4
15
Corundum
Al2O3
16
Graphite
C
17
Diamond
C
18
Lonsdaleite
C
19
Figure 2. Canyon Diablo meteorite, Barringer Meteor Crater region, Coconino County, Arizona. Note the sculpting of its form by ablation and loss of the molten surface layer of iron alloy formed by frictional forces during its fall through the air.
Figure 3. Etched slice of a Canyon Diablo meteorite, Barringer Meteor Crater Region, Coconino county, Arizona[Ref28]. Note both the brown crystal of troilite with a grey rim of cohenite and the The angular Widmenstatten are comprised of angular interleaving bands of the iron-nickel alloys kamacite and taenite referenced in TABLE 1.
The Structure and Metallurgy of Iron-Nickel Meteorites
Iron-nickel meteorites are thought to be remnants of the cores of planetesimals following collision between them . With slow cooling during solidificaiton of the core the liquid alloy mixture of iron and nickel results in a mixture of the two minerals kamacite and taenite. With sufficiently slow cooling to 912 deg C and below discrete visible crystals of each mineral form separately as shown in the iron-nickel phase diagram. The interleafed arrangement of the crystals results in the arrangement called Widmanstatten Figures as shown in Figure 3 which become visible upon etching with an acid. The different grey-tones of the crystals develop from different etching susceptibilities which arise from the different atomic arrangements within face-centered cubic kamacite and body-centered cubic taenite.
Structure, Mineral Composition, and Formation of Stony-iron Meteorites
Stony-iron meteorites consist of approximately equal parts of iron-nickel alloy and silicate minerals as opposed to stony meteorites which primarily are made up of silicate minerals. Stony-iron meteorites are divided into two groups, the pallasites and the mesosiderites Pallasites have silicate minerals, mostly olivine embedded in the meteoric iron. Mesosiderites are breccias comprised of fragments of meteoric iron interspersed with fragments of silicate minerals.
Pallasites
Results of a recent study suggest that pallasite meteorites may have formed in a glancing impact between a body with a largely solidified core surrounded by a molten layer and a larger body. It is assumed that loss of the solid core and formation a body comprised of aggregates of fragments of olivine surrounded by molten iron-nickel alloy ensued. Solidification of the molten alloy results in cementation of the olivine fragments which results in the structure shown in Figure 4
Figure 4. The olivine usually is present in a 2/1 volume ratio with the iron-nickel matrix. The boundary regions between an olivine crystal and metal may contain thin layers of a mineral such as troilite, schreibersite, or chromite.
Mesosiderites
Mesosiderites are considered to have formed from fragments of iron-nickel alloy and silicate minerals which resulted from collision of metal-rich and silica-rich asteroids. The fragments may be of the igneous rocks, basalts, gabbros, and pyroxenites of igneous rocks as well as fragments of the minerals orthopyroxene, olivine, and plagioclase. The Iron-nickel metal is mostly in the form of millimenter or sub-millimeter grains admixed with grains of silicate minerals in the same size range surrounding the larger fragments of rocks and minerals. These structural features are shown in Figure 5.
Figure 5 . Mesosiderite, found at Gillio, Libya in 1985. Metal nodules, pyroxene, on Ca-pyroxene fragments, plagioclase, pyrrhotite, chromite, and both kamacite and taenite are present.
Both precious red and black corals are bottom-dwelling sessile marine branched animals that have been harvested at depths between 60 and 20,000 feet [Ref 1, Ref 2]. They have provided lapidarists and other artisans with materials they use to create extraordinarily beautiful jewelry and objects of art, as witnessed by Figures 1 and 2. In this Blog, I’ll describe the physical properties and the sources of the colors of the corals that underlie their use in jewelry making and in carving fine objects of art.
As shown in Figure 1, the Chinese Qing Dynasty red coral sculpture, featuring four carved figures of Buddha, capitalizes on the flowing branched nature of the coral to produce a beautiful and graceful carving. The flowing shapes of the branches
of black coral are an interesting contrast to the disciplined shapes of the gold fittings set with gems, as seen in Figure 2.
Figure 1. Chinese Qing Dynasty carving in branched red coral with four figures of Buddha, circa 1862-1874 [Ref 3].Figure 2. Black coral necklace with accents of green and pink tourmaline, blue topaz, amethyst, citrine, and fire opal set in 18-carat gold [Ref 4].
PROPERTIES OF PRECIOUS RED AND BLACK CORALS
Gemstones of red and black coral comprise the hard tissue core or skeleton which supports the soft tissues of the organisms as shown in Figures 3-5.
Figure 3. A red coral in situ with white soft tissue supported by the red coral tree. The soft tissue contains the polyps, the feeding organ of the coral and tissues connecting them [Ref 5].Figure 4. Sections of branches of the red coral skeleton. The section on the left has been bleached. The furrows on the surface of the skeleton contain the part of the soft tissue which distributes nutrients [Ref 6].Figure 5. A black coral (Cirrhipathes sp.) with yellow soft tissue surrounding the hard tissue core is shown on the left and the same specimen with its soft tissue removed is shown on the right [Ref 7].
PROPERTIES OF PRECIOUS RED AND BLACK CORALS
Gemstones of red and black coral comprise the hard tissue core or skeleton which supports the soft tissues of the organisms as shown in Figures 3-5. The physical and chemical properties of each coral underlie its usage in jewelry and art objects.
Physical and Chemical Properties of Precious Red Coral
The hard tissue of the skeleton of red coral is comprised of aggregated nanometer-sized crystals of magnesium-rich calcite {(Ca.Mn)CO3} which are arranged in rings separated by an annular layer of organic matrix containing glycoproteins and glycosaminoglycans[Ref 8]. The annular arrangement of the mineral and organic matrix is shown in the cross-section of a stem in Figure. The organic matrix is highlighted by a purple stain and the layer of magnesium-rich calcite is unstained [Ref 9]. The axial region rich in magnesian calcite is indicate by the letter
A and the spaces occupied by the longitudinal canals, the regions of soft tissue which transport nutrients are labeled by the letter B.
Figure 6. Cross-section of a stem of red coral in which the soft tissue has been stained purple [Ref 10].
Pigmentation in Precious Red Coral
The red pigment in precious red coral has been determined to be canthaxanthin, a member of the family of retinoids which are ubiquitous in red-colored organisms [Ref 11]. Its location in the outer soft tissue and organic matrix is demonstrated by its red color in Figures 7 and 8. The range of hues of the red color of the coral as a gemstone is shown in Reference 12.
Figure 7. The localization of the red pigment canthanxanthin in the organic matrix is demonstrated by the lack of color in the sclerites (spicules) [Ref 10].Figure 8. Further demonstration that the red pigment is present in the organic matrix [Ref 13].
Mechanical Properties of Precious Red Coral [Ref 14]
The values of Mohs Hardness in the range 3-4 for red coral are comparable to that of 3 for black coral [Ref 14]. With its axial core of magnesian calcite, red coral is brittle with an irregular or splintery fracture, and cannot be bent to assume complex shapes as can be done with black coral. Natural shapes and those obtained by carving are similar to those in black coral jewelry and art objects as can be seen in comparing the jewelry and art objects in Figures 9-17 to those in Figures 18-26.
RED CORAL JEWELRY AND ART OBJECTS
Figure 9. Necklace incorporating branches of red coral [Ref 15].Figure 10. Red coral bracelet with gold fittings [Ref 16]. Figure 11. Italian good-luck-horn pendant [Ref 17].
Figure 12. Goddess Flora carved in red coral [Ref 18].
Figure 13. Red coral necklace with silver beads, Yemeni [Ref 19].
Figure 14. Figure of Mulan carved in red coral [Ref 20, Ref 21].Figure15. Carved flower pendant set in 14 carat gold [Ref 22].Figure 16. Red coral rose set in sterling silver ring [Ref 23].
Figure 17. Carved red coral snuff bottle. Chinese [Ref 24].
Physical and Chemical Properties of Black Coral
Some black corals are branched, while others have long and straight stems or spirally twisted stems, as shown in Figures 18 and 19. The stem or branch of the black coral skeleton is not composed of a core of magnesian-rich calcite as in red coral, but consists of laminated composites comprised primarily of protein and chitin fibrils [Ref 24]. The growth of the diameter of a stem or branch proceeds by accretion of layers, as shown by the polished cross section of a stem in Figure 18 [Ref 25]. The black color seen throughout the stem is due to the melanin [Ref 25], a black pigment widely distributed in both the animal and plant kingdoms [Ref 26].
Figure 18. Branched black coral [Ref 27].Figure 19. Spiral black coral with and without the external tissues which resides on the central skeleton [Ref 28].
Figure 20. Transverse polished section of black coral. (Leiopathes species) showing layers of chitin after removal of proteins. The fine structure of concentric rings is evident. The diameter of the stem is ~ 7 mm {Ref 29].
Mechanical Properties of Black Coral
To compensate for the lack of stiffness, due to the absence of a skeletal core of rigid magnesium, as in red coral layers, the chitin fibrils [Ref 30] comprising the strong part of the skeleton, is spirally wound in the concentric layers [Ref 30] comprising the stem and branches as shown in Figures 8-10. Such a winding scheme works to prevent kinking of the stem due to bending and twisting of the stem due to torsional forces. This scheme compensates for the lack of a stiff mineral axis as is present in red coral. Values of the mechanical measures of the strength of the skeleton of black coral are summarized in Table I taken from Ref 30.
Figure 19. View of two layers of chitin fibrils in two layers the stem of black coral. The fibrils are wound in spiral fashion about the axis of the stem. The scale bar is 10 microns (0.0010 cm) [Ref 30].
Figure 20. Sketch showing different spiral patterns in layers of chitin fibrils in two black coral species [Ref 30].
TABLE I MECHANICAl PROPERTIES OF SKLETONS OF TWO SPECIES OF BLACK CORAL (Antipathians)[Ref30]
PROPERTIES
ANTIPATHES FIORDENSIS
ANTIPATHES SALIX
Mohs Hardness
3
3
Micro-indentation Hardnesshardness along the long axis (pounds/mm2)
26,000 lb/in2
31,663 lb/in2
Micro-indentation hardness along a diameter (pounds/mm2)
28,968 lb/in2
32,516 lb/in2
Extensibility (%)
7.37
3.84
The Mohs hardness of 3, of black coral, is comparable to the range of values 3-4 of red coral, so that expectations of resistance of both to wear, particularly scratching are similar. Values of micro-indentation hardness in the range of 26,000 to 32,516 lb/in2 are approximately one-half the value of 58,064lb/in2 estimated for the rhombohedral surface of calcite estimated from Figure 1. These values of Mohs and micro-indentation hardness suggest care in wearing black coral jewelry. Jewelry such as pendants, earrings, and necklaces of this coral will have longer scratch-free life expectancy.
The large room-temperature values of the extensibility of the two black coral species of 3.845% and 7.37%, especially augmented by the thermoelasticity, [Ref 31], of the coral at higher temperatures underlie the shaping of jewelry with intricate shapes. The softness of black coral underlies the use of carved shapes in jewelry. Working the coral at an elevated temperature would further enable attaining intricate shapes with finer carved relief.
Figure 18. Transverse polished section of black coral. (Leiopathes species) showing layers of chitin after removal of proteins. The fine structure of concentric rings is evident. The diameter of the stem is ~ 7 mm [Ref 32].
Figure 21. Black coral cuff obtained by bending [Ref 33].
Figure 22. Turtles carved in black coral set in gold [Ref 34].
Figure 23. Galloping steed carved in black coral [Ref 35].
Figure 24. Flowing shape carved in black coral and set in gold [Ref 36].
Figure 25. Dragon bracelet fabricated by carving and bending black coral [Ref 37].
Figure 26 Miniature caravel with hull fabricated by carving and sails fabricated by both carving and bending black coral [Ref 38].
Art Deco is my favorite style of jewelry, with its flair of design and the use of unusual combinations of gemstones. Art Deco is a style of architecture and design which first appeared in France just before World War I, reached its high point during the 1925 Paris Exposition of Decorative Arts, and extended into the 1940’s. Today, authentic Art Deco period jewelry and art objects, as well as reproductions, remain esteemed by wearers of jewelry and collectors. In the following gallery I’ve included ruby jewelry and art objects which greatly appeal to me.
RUBY JEWELRY AND ART WORKS GALLERY
Figure 1. Art Deco brooch with carved ruby and surrounding diamonds [Ref 1].Figure 2. Art Deco diamond and ruby floral cluster setting in a platinum ring [Ref 2].Figure 3. Art Deco ruby and diamond decorated onyx compact [Ref 3].Figure 4. Art Deco carved ruby and emerald, diamond, onyx, and enamel pendant brooch [Ref 4].Figure 5. Art Deco carved jade, diamond, ruby, and platinum card case [Ref 5].Figure 6. Art Deco ruby and diamond necklace and brooch [Ref 6].Figure 7. Art Deco ruby, onyx, and diamond set platinum brooch [Ref 7].Figure 8. Art deco carved ruby, sapphire, emerald, and diamond “Tutti Frutti” bracelet [Ref 8].Figure 9. Art Deco ruby and diamond yellow gold watch [Ref 9].Figure 10. Art Deco carved jade, ruby, and onyx Pendant brooch [Ref 10].
Summit Fire District Station 31 6425 N Cosnino Rd, Flagstaff, AZ corner of Townsend-Winona & Cosnino roads
Agenda:
Along with the usual club business, the meetings consist of discussions of upcoming field trips, local club shows, ‘show and tell ‘of members’ recent finds and expositions. As always the club library is available for browsing and snacks for munching.
Fieldtrips are generally scheduled on the Saturday after the monthly meeting. The plans for the fieldtrip are discussed at that meeting. Details include time and location for caravaning to the search site, types and examples of specimens we’ll be looking for, location map, and any personal items needed for the exposition.
Anyone who plans on participating on the club sponsored trip needs to be a member.
January Fieldtrip
The club did not plan a trip for January. However, they agreed that the Quartzsite Show would be the destination for those who could make it. The show runs through January and February. Information for the show may be found if you Google “Quartzsite Gem and Mineral Showcase”.
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