MINERAL STUFF: THE GEMSTONE JADE

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 (5^th – 4^th 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 13^th 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, 13^th – 16^th
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

Minerals in Minor Quantities	Mineral in Minor quantity
diopside, grossularitic garnet, magnetite, chromite, graphite, apatite, rutile, pyrite, datolite, vesuvianite, prehnite, talc, serpentine, and titanite.	Diopside, also a pyroxene

Properties of Jade As a Gemstone

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⁺ (⁴E_g)-> ⁵T_2gand by the excitation and decay of a constituent iron ion, chromium ion Cr³⁺ (⁴A₂) ->⁴T_2,, 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 O^2- -> 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⁺, O^2-, OH^1-	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 10²	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].

REFERENCES JADE

Ref 1. https://www.mindat.org/min-10403.html

Ref 2. https://www.ancient.eu/article/1088/jade-in-ancient-china/

Ref 3. https://www.jadeite-atelier.com/blogs/jade-articles/history-of-jade-in-mesoamerica

Ref 4. https://www.ancient.eu/Olmec_Civilization/

Ref 5. https://www.ancient.eu/Maya_Civilization/

Ref 6. https://www.ancient.eu/Aztec_Civilization/

Ref 7. https://en.wikipedia.org/wiki/M%C4%81ori_people

Ref 8. https://teara.govt.nz/en/pounamu-jade-or-greenstone

Ref 9. https://www.ancient.eu/image/6778/zhou-dynasty-jade-dragon/

Ref 10. https://www.metmuseum.org/art/collection/search/310279