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HARDNESS: A MECHANICAL PROPERTY OF USE IN IDENTIFYING MINERALS

Along with the colors and crystal forms of minerals, their mechanical properties such as the hardness. tenacity, and habits of structural failure can be very useful tools in identifying an unknown mineral. In this first Blog on the use of mechanical properties in identifying minerals I’ll focus on hardness and describe the Moh’s Hardness Scale, the standard reference scale for minerals, and briefly describe how to use it. I’ll also list those often available objects which can be usedinstead of a mineral member of the scale as hardness references for comparison with the mineral.

The Mohs Hardness Test and Scale were invented in 1812 by the German mineralogist Fredrich Moh[Ref1,2] as a means to rank minerals according to their relative hardness in resisting scratching. Its ease of use has resulted in its wide application by mineral collectors and lapidarists. The ten-point scale begins with the softest mineral talc assigned a hardness of 1 and ends with the hardest mineral diamond assigned a hardness of 10. Minerals with intervening hardness values between 2 and 9 are: gypsum (selenite) at a hardness of 2, calcite at 3, fluorite at 4, apatite at 5, orthoclase (feldspar) at 6, quartz at 7, topaz at 8, and corundum (ruby, sapphire) at 9. In Figure 1 shows the hardness scale, and as well, includes everyday objects of known hardness which can also be used in hardness testing[Ref2]. The relative hardness values are obtained by determining which mineral scratches one of lesser hardness and is scratched by a mineral or an object of greater hardness. Testing is done by placing a sharp point of one mineral or another testing agent against the surface of another and attempting to scratch it. One of the following results may be observed:

If mineral A scratches mineral B then A is harder than B.

If A doesn’t scratch B then B is harder than A.

If A and B are relatively ineffective in scratching each other they are of equal hardness.

If A can be scratched by B but not by C the hardness o A is between the hardness of B and C.

The Mohs Hardness Test is performed using the steps and tips as described in

Figures 2 and as shown live in the YouTube video accompanying this brief presentation. An example of testing using a knife and a penny are described in Figure3.

Figure 1. Mohs Hardness Scale collection and mineral identification[Ref3]. The copper penny must be dated no later than 1982; pennies issued subsequently were minted using a softer bronze alloy[Ref4].
Figure 2. Steps in performing Mohs Hardness Test[Ref5].
Figure3. An example of a Mohs Hardness test using a knife and a penny[Ref5].

REFERENCES

Ref 1. https://en.wikipedia.org/wiki/Friedrich_Mohs

Ref2. https://geology.com/minerals/mohs-hardness-scale.shtml

Ref 3. https://www.lindahall.org/friedrich-mohs/

Ref 4. https://www.nbc12.com/story/17003531/jens-coin-story/

Ref 5. http://www.rocksandminerals.com/hardness/mohs.htm

Sapphire – Art Deco

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, reaching its high point in the 1925 Paris Exposition of Decorative Arts, and extending into the 1940s.  Today, authentic period jewelry, art objects and reproductions remain esteemed by those who wear and collect it.  In the following gallery I’ve included jewelry and art objects which greatly appeal to me.

SAPPHIRE JEWELRY AND ART WORKS GALLERY

Figure 1.  Art Deco brooch with sapphire cabochon set in an onyx frame with rubies set in gold.  The material on which the gems are mounted is not identified [Ref 1].
Figure 2.  Art Deco sapphire and diamond inlayed silver cigarette case [Ref 2].
Figure 3.  Art Deco diamond and sapphire ring [Ref 3].
Figure 4.  Cuff links with ruby cabochon and sapphire set in white gold with black onyx trimmed stud [Ref 4].
Figure 5.  Art Deco diamond, sapphire, and platinum watch [Ref 5].
Figure 6.  Art Deco tiara with diamonds and sapphires set in white gold [Ref 6].
Figure 7.  Art Deco diamond and sapphire bracelet, circa 1920 [Ref 7].
Figure 8.  Art Deco brooch in Egyptian style set with sapphires, emeralds, and diamonds [Ref 8].
Figure 9.  Diamond brooch set with sapphire accents [Ref 9].
Figure 10.  Art Deco watch with cameos, set with sapphires and diamonds [Ref 10].

REFERENCES

Ref 1.  http://www.doitjewelry.com/02/21/a-beautiful-and-rare-art-deco-brooch-french-circa-1930-centring-a-round-sapphire-cabochon-within-an-onyx-frame-and-further-set-with-calibre-rubies-mounted-in-gold-illegible-makers-mark-6-x-3c-3/

Ref 2.  https://www.rubylane.com/item/821070-RT-4365/Art-Deco-Diamond-Sapphire-800-Silver

Ref 3.  http://www.antiquejewel.com/en/2ndpage.asp?dtn=15033-0048

Ref 4.  https://www.pinterest.com/pin/383861568224232322/

Ref 5.  http://www.macklowegallery.com/search-antiques.asp/currentPage/-1/art-nouveau-antique-estate/art%20deco

Ref 6.  https://www.pinterest.com/pin/368732288212254566/

Ref 7.  https://www.langantiques.com/university/Art_Deco_Era_Jewelry

Ref 8.  http://www.gemscene.com/art-deco.html

Ref 9.  https://www.google.com/search?hl=en&biw=1180&bih=952&tbm=isch&sa=1&ei=4SMEXPngL4LMjgSM7IKgBA&q=sapphire+jewelry+and+art+made+in+art+deco+era&oq=sapphire+jewelry+and+art+made+in+art+deco+era&gs_l=img.12…8687.29358..31068…3.0..0.98.2380.32……0….1..gws-wiz-img.cb574UrAC_k#imgrc=ROK8ATGFQOWIgM:

Ref 10.  http://www.antiquejewel.com/en/2ndpage.asp?dtn=13119-0030

Ancient Sapphires

In this blog I’m displaying examples of jewelry and art objects from ancient Asia and the Mughal Empire.  I also include examples of jewelry from the Roman Empire and the Medieval Victorian Eras in Europe.

ANCIENT ASIAN

Figure 1.  Sapphire and gold finger ring, Central Asian, circa 4th century BC – 1st century AD [Ref 1].
Figure 2.  Various types of beads found in burial grounds dated to 1000 BC in Sri Lanka [Ref 2].
Figure 3.  Turban ornament set with sapphires, emeralds, rubies, 
from the Mughal Empire, created after 1526 [Ref 3, Ref 4].
Figure 4.  White jade scent bottle set with sapphires, rubies, diamonds, and emeralds set in gold, Mughal Empire,18th/19th century [Ref 5].
Figure 5.  Gold turban ornament set with a sapphire
cabochon with other gems of rubies and emeralds, 
Mughal Empire [Ref 6]

ANCIENT ROMAN EMPIRE

Figure 6.  Roman sapphire cameo with gemstone source attributed to Sri Lanka,
1st century AD [Ref 7].
Figure 7.  Roman sapphire and gold ring, Sri Lankan, circa 1st -2rd century AD [Ref 8].
Figure 8.  Roman sapphire in gold earrings.  The other gemstones are not identified [Ref 9].
Figure 9.  Roman sapphire and gold dress pin carved from a single crystal, 
100-130 AD [Ref 10].
Figure 10.  Roman gold bracelet with sapphire, emerald, and glass settings, 375-400 AD [Ref 11].

MEDIEVAL EUROPEAN

Figure 11.  Sapphire and gold ring with beading characteristic of the Viking period, 10th-11th centuries AD [Ref 12].

RENAISSANCE EUROPE

Figure 12.  Brooch set with sapphires, garnets, pearls, and enameled, German, 1359 AD [Ref 13].

Figure 13.  Carved sapphire seal mounted in enameled gold, England, Circa
1580 AD [Ref 14].

VICTORIAN ENGLAND (EUROPE)

Figure 14.  Sapphire, diamond and gold cross, Russia, 1898 [Ref 15].

REFERENCES

Ref 1.  https://onlineonly.christies.com/s/ancient-jewelry-wearable-art/central-asian-gold-sapphire-finger-ring-30/63724

Ref 2.  https://www.internetstones.com/ancient-technology-sri-lankan-gemstone-beads-carvings-cameos-intaglios-carnelian-rock-crystal.html

Ref 3.  http://portobelloantiques.blogspot.com/2010/05/indian-turban-ornament.html

Ref 4.  https://en.wikipedia.org/wiki/Mughal_Empire

Ref 5.  https://www.reenaahluwalia.com/blog/2013/6/20/splendors-of-mughal-india-i

Ref 6.  https://bellatory.com/fashion-accessories/Mughal-Jewelry-Royal-and-antique-jewelry-of-North-India

Ref 7.  https://gem-a.com/news-publications/media-centre/news-blogs/gems-from-gem-a/gem/ancient-sapphires-and-adventures-in-ceylon

Ref 8.  https://medusa-art.com/roman-gold-ring-with-sapphire.html

Ref 9  https://www.google.com/search?q=ancient+roman+sapphire+jewelry&hl=en&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjMy_OcqYTfAhVOEawKHW4EAxkQ_AUIDygC&biw=1236&bih=951#imgrc=BNm3q6dbCiYfDM:

Ref 10.  https://www.pinterest.com/pin/82824080622310428/

Ref 11.  http://www.getty.edu/art/collection/objects/16310/unknown-maker-bracelet-roman-about-ad-379-395/

Ref 12.  http://www.thehistoryblog.com/archives/12180

Ref 13.  https://www.pinterest.com/pin/229050331032972074/

Ref 14.  http://collections.vam.ac.uk/item/O114861/seal-and-case-unknown/

Ref 15.  http://romanovrussia.com/antique/1800s-sapphire-cross/

Quartzite Field Trip

Four members of the club (Linda and Marty Dougherty and John and Beth Duggan) made it down to Quartzite, Arizona for the annual Pow Wow. This show has been held in January for over 50 years. There were over two thousand vendors to visit in the area so there was lots to see and buy.

For the seventh year in a row Linda and Marty attended the annual roadside Clean up in Quartzsite, Arizona sponsored by the Bureau of Land Management and American Lands Access Association. There were club members of other American Federations, Northwest, California, Mid-west and Rocky Mountain, which the Coconino Club is a member.

Twelve of them plus the cameraman drove 10 miles East of Quartzsite to the Gold Nugget Rd.  turn-off and spent a couple hours collecting discarded trash which is apparent in the attached photograph. Not sure how much this years weighed, but in previous years in this area we collected a couple tons of trash, some being really gross!!!!

Marty and Linda are on the left

Largest Star Sapphire/Ruby

We usually think of star sapphires and rubies as stones in the few carat range, not in hundreds and thousands of carats. But some are an amazing size. At the top, are the World’s Largest which are truly awesome. In this blog I’ll describe the worlds largest blue star sapphire, star ruby, and black star sapphire, as well as gems ranking near their size but just below the record. I’ll also include a short history of each gem. 

Worlds Largest Blue Star Sapphire: The Star of Adam [Ref 1, Ref 2]

The world’s largest star sapphire weighs an amazing 1,4O4 carats, and when held, largely occupies the palm of a hand, as shown in Figure 1. 

Figure 1. Star of Adam

The stone was found in the fall of 2015 at mine in the famed alluvial gem deposits near Ratnapura, Sri Lanka [Ref 1 Ref 2]. At first sight, the owner estimated the value of the gem at $175 million. As of January 2016, the owner was pondering whether to auction the gem or to display it. A diligent trip over the internet disclosed no further information about any attempt to auction the gem. However, the gem may have been sold in a private transaction.

World’s Largest Black Star Sapphire: The Black Star of Queensland [Ref 3, Ref 4, Ref 5]

The Black Star of Queensland, as shown in Figure 2, weighs 733 carats, and was the world’s largest sapphire until being displaced by the Star of Adam. This gem is also seen to fill the palm of a hand but does not have the cabochon height of the Star of Adam.

Reportedly, the rough stone was found by a twelve-year old boy, Roy Spencer, in the mid-1930s, in the Reward Claim near Anakie, Queensland, Australia [Ref 3]. The boy’s father, Harry Spencer, assumed it was merely a black crystal and the family used it as a doorstop for over a decade. A second look disclosed the gem.

The stone was sold by Spencer in 1947 to the jeweler Harry Kazanjian for $18,000AU which funded a new house for the family. The subsequent history of the stone has been shared by owners and institutions. The gem was loaned to the Natural History Museum of the Smithsonian Institution in 1969. In 1971 it was seen around Cher’s on television show. To fulfill a childhood dream, the artist and jeweler, Jack Armstrong, and his wealthy girlfriend, Gabrielle Grohe, convinced the Kazanjian family to sell the gem in 2003 [Ref 4]. In 2010 [Ref 5], the pair squabbled over the stone and Armstrong agreed to pay $500,000 for Grohe’s share,  but failed to pay, and due to a judge’s ruling he lost all right to the gemstone. 

Figure 2. Worlds largest black star sapphire [Ref 6].

World’ Largest Star Ruby: the Appalachian Ruby Star [Ref 7]

The Appalachian Ruby Star weighs 139.43 carats and barely edges out the Rosser Reeves Star ruby, that weighs in at 138.72 carats, as shown in Figure 3. The Appalachian Star ruby was cut from a rough ruby, which also yielded three additional stones. The weight of the group of four star rubies became known as the Mountain Star Ruby Collection and is shown in Figure 4. The aggregate weight of the rubies totals 342 carats.

The rough ruby was found in 1990 by Wayne Messer, a fishing guide in Western North Carolina. He had noted traces of corundum in a stream bed and traced the alluvial stones back to their source. Upon digging some eight feet, found the rough ruby. The quartet of star rubies was cut by Sam Fore from the rough stone which weighed 377 carats.

The Appalachian Star ruby was exhibited in 1992 at the Natural history Museum in London, drawing an estimated 150,000 people. Several attempts were made over the years to sell the collection, appraised at a value close to $100 million. Only recently, following the death of Messer, was the collection offered for sale.

Figure 3. The Appalachian Star, World’s Largest Star ruby [Ref 7].


Figure 4. The four star rubies, cut from the large rough ruby which gave the Appalachian Star [Ref 7].

The Rosser Reeves Ruby [Ref 8, Ref 9]

At a weight of 138.7 carats, the Rosser Reeve Ruby is the world’s second heaviest star ruby, and was found in Sri Lanka. The gem is named after Rosser Reeves a pioneer in the advertising industry. Rosser donated the gem to the Smithsonian Institute in 1965. Despite his attractive tale of buying the gem at an auction in Istanbul, he actually bought the gem from Robert C. Nelson Jr.  At purchase, the stone weighed just over 140 carats, but was scratched and so was re-polished, which also helped to re-center the star on the Cabochon. Fortunately for museum goers, this beautiful gem still can be seen at the Smithsonian institute. As a note, the Wikipedia article used as the reference for this segment of the blog was written by Brendan Reeves, great grandson of Rosser.

Figure 5. The Rosser Reeves star ruby [Ref 9].

REFERENCES

Ref 1. https://www.forbes.com/sites/trevornace/2016/01/10/worlds-largest-blue-star-sapphire-found-worth-300-million/#6a06d4f075d1

Ref 2. https://www.mindat.org/loc-3147.html

Ref 3. https://en.wikipedia.org/wiki/Black_Star_of_Queensland#cite_note-5

Ref 4. https://www.upi.com/Feature-Legendary-sapphire-for-sale/10481044491153/

Ref 5. http://articles.latimes.com/2010/jan/05/local/la-me-blacksapphire5-2010jan05/2

Ref 6. https://www.pinterest.com/pin/863987509737025682/

Ref 7. https://www.mnn.com/earth-matters/wilderness-resources/blogs/extremely-rare-star-rubies-found-fishing-guide-could-fetch-millions

Ref 8. https://en.wikipedia.org/wiki/Rosser_Reeves_Ruby

Ref 9. https://geogallery.si.edu/10002811/rosser-reeves-star-ruby

October 26th Field Trip to Alpine Az

This was the clubs second field trip for October with the intention of collecting Luna Blue Agate in New Mexico.

A new friend from the Prescott club was to meet us Saturday afternoon  in Alpine to lead us to Reserve , New Mexico to collect Agate on Sunday October 27th.

Thirteen members arrived in Alpine, Arizona around noon at the motel and from there we headed east on the 180 towards Luna N.M. We made several stops south of Luna at mile marker 10 and then at mile marker 4. 

Good material was collected at MM4  in the road cuts, some Luna Blue was found and Druzy. Not a real productive site but still a good start for what awaited in Reserve on Sunday.

After breakfast Sunday morning we followed Allen Valley to Reserve N.M. where Allen had made arrangements to cross over private property onto State Land which was about a 3 mile drive uphill on uneven dirt road through three closed gates to a plateau in a forested setting. A vast expanse of forest land was covered in Banded Agate with Druzy. It was an overwhelming amount of material. It was hard not to pick it all up, but we had to be selective when we realized how much there actually was.

We spent the day there trying several locations and coming away very happy. 

Sunday evening at dinner Allen made arrangements with a local from Alpine to lead us back into N.M. to several locations that turned out to be not so productive. It is my feeling our local guide did not want to take us to any secret spots thinking we would come back at some point and clean them out, can’t blame her for that, but she shouldn’t have offered to waste a whole day driving around. Beautiful country but we wanted rocks too. All in all this was a successful trip.

Members that attended :

Lowen & Cheryl

Sandy & Wendy

John & Beth

Andrea & Linda A

Clint & Erica 

Alan Cartwright 

Marty & Linda

OCTOBER 19TH CLUB FIELD TRIP TO SYCAMORE CREEK, ARIZONA

Saturday morning a group of 12 signed in for the two and a half hour drive south to Sycamore Creek.   We met Larry Jensen who led our group on a 2 mile dirt road where we all found places to safely pull to the side of the road at a dry wash to search for Red Jasper. Weather was warm and comfortable.

Being a Saturday there were many dirt bikes traveling the road as well as weekend campers to keep us busy. Most of the group canvased the wash area for Jasper and a few of us brought out the 15 pound sledge hammer and steel chisels to assist breaking apart  rocks suspected to be hiding  good cutting material. I saw members carrying 5 gallon buckets of Red Jasper back to their vehicles so I assume we all found a little something to work with.

Next time when we return I would prefer a weekday trip as there are three locations to collect material and we only saw the first site because of the off-road vehicle traffic.

 Attending Members:

Alan & Linda

Clint & Erica

John & Beth

Rob & Sue

Alan Cartwright

Kathy S

Marty & Linda

Corundum – From Sapphires to Rubies

Gemstones of the mineral corundum [Ref 1] offer a rainbow of colors for the lapidarist and jewelry maker as displayed in Figure 1. 

Traditionally, of these, the ruby and blue sapphire, along with diamond and emerald, are considered to be the four-membered family of precious gems.  Corundum gemstones, other than the ruby and blue sapphire, are also considered sapphires, having colors ranging from green to pink.

In this blog, I’ll describe the crystallography of corundum, and the physical and optical properties of corundum, including the sources of the colors in its gemstones. I will also present a gallery of ruby and sapphire mineral specimens.

Figure 1. A rainbow of the gemstones from corundum: ruby, blue sapphire, and green to pink sapphires.

CRYSTALLOGRAPHY OF CORUNDUM [Ref 1]

Crystal System of Corundum

Corundum crystallizes in the Trigonal System, which has three axes in a plane and are arranged at 120 degrees to each other, with an axis perpendicular to the plane, as shown in Figure 2. Of the typical forms of crystals shown in the figure, corundum frequently crystallizes as a hexagonal prism, terminated by the basal pinacoid; as a bipyramid, the hexagonal prism is terminated by a bipyramid; the rhombehedron and the hexagonal prism are terminated by the rhombehedron, and the schalenohedron. Examples of corundum crystals taking these forms are shown in Figures 5-11. Figure 7 shows a diagram of a crystal exhibiting all of these forms except the rhombohedron and schalenohedron. The latter form is shown by the sapphire crystal in Figure 10.

Figure 2. The four axes of the trigonal crystal system
Figure 3. Properties of the Trigonal Crystal System
Figure 4. Crystal of corundum with typical forms; only the schalenohedron is not shown.

Twinning in Corundum [Ref 1].

Multiple twinning on the rhombohedral plane with laminar structure with striations on both the basal pinacoid perpendicular to the c-axis and the hexagonal prism or on bipyramid faces, as shown by the terminated bipyrimidal sapphire crystal, shown in Figure 10 [Ref 12]. Corundum is also twinned on the hexagonal prism faces of tabular crystals exhibiting an arrowhead shape, as shown by the sapphire specimen in Figure 11[Ref 13]. The view is at the base of the arrowhead shape and pointing towards the tip. Less frequent twinning in corundum occurs on the basal pinacoid, perpendicular to the long axis of the crystal, as showing repetitive twinning along its length in Figure 12. 

The view is at the base of the arrowhead shape and pointing towards the tip. Less frequent twinning in corundum occurs on the basal pinacoid, perpendicular to the long axis of the crystal, as showing repetitive twinning along its length in Figure 12. 

The view is at the base of the arrowhead shape and pointing towards the tip. Less frequent twinning in corundum occurs on the basal pinacoid, perpendicular to the long axis of the crystal, as showing repetitive twinning along its length in Figure 12. 

MECHANICAL PROPERTIES OF CORUNDUM [Ref 2]

The high values of hardness and ultimate strength and its resistance to cleavage, underlie the toughness of corundum gemstones and their wide usage in rings and bracelets, both susceptible to impact while worn. Values of the strength factors of corundum are summarized in TABLE I.

                      TABLE I. STRENGTH FACTORS OF CORUNDUM GEMSTONES

PROPERTYVALUE/OBSERVATIONREFERENCE
Mohs Hardness SCALE9 (Member of scale)11
Ultimate Compressive Strength435,000 psi13
Ultimate Tensile Strength43,500 psi13
Flexural Strength58, 00013
TenacityBrittle11
FractureIrregular/Uneven,
Conchoidal
11
CleavageNone Observed11

OPTICAL PROPERTIES OF CORUNDUM [Ref 1]

The Refractive Index values of corundum lie in the ranges 1.759-1.772 depending on direction of light polarization. These values are considerably below the value of 2.418 for diamond [Ref 3], and underlies the beauty of corundum gemstones being in their vivid colors and not in brilliance or fire.

The light reflected from the surface, without penetration into gemstones is colorless, as often seen in photographs of gemstones, as in Figure 14.

Light scattering from oriented needle-like crystals of rutile, or to colloidal or other material in oriented tubules is observed in the star sapphire and star ruby as described in another blog on star rubies and sapphires [Ref 4].

Figure 14. Reflections from the surface of the ruby gemstone are colorless, while those reflected from the back of the stone are colored.

SOURCES OF COLOR IN CORUNDUM GEMSTONES

Corundum is aluminum oxide, with the formula Al2O3. Each trivalent aluminum Al3+ ion is surrounded by six oxygen ions, located at the tips of an octahedron in the crystal lattice of corundum, shown in Figure 15. Defects in the forms of ions of metal impurities substituting for the aluminum ion, are responsible for the colors of corundum [Ref 5 ]. The impurity metal ions and the associated colors are summarized in Table I, shown in Figure 4. The divalent and trivalent ions substitute for the aluminum ion in the lattice of the corundum lattice.

Figure 15. Crystal lattice of corundum.
Figure 4. Sources of colors in corundum gemstones. See legend for terms below.

Legend for Figure 4
Cr3+ = Trivalent chromium ion 
Fe3+ = Trivalent iron ion
Fe2+ = Divalent iron ion
Ti4+ = Tetravalent titanium ion
O1-V = neighboring monovalent oxygen ion O1- and lattice vacancy V in lattice
            taking the place of an Al3+ ion.
Al3+ = Trivalent aluminum ion

COLOR CHANGES IN HEAT TREATED SAPPHIRES

Consideration of the various colors in natural sapphires, having different combinations and concentrations of the ions and ion pairs, before and after their heat treatment, serves to demonstrate their effects on color in corundum gemstones. The results of heat treatments are shown in Figures 16-18.

Some sapphires are heat treated to improve the attractiveness of their colors. Studies were carried out to identify changes in concentrations of ions that led to improvements in the aesthetics of the gem stone. The studies showed two major effects in the brown-toned sapphires and in the optical absorption spectrum of sample rO 4/5, red orange. The red trace of the absorption spectrum shows increased absorption due to the chromium ion, a decreased absorption due to trivalent iron ion pairs contributed from paired divalent and trivalent iron ions and single trivalent iron ions. The heat treatment resulted in an increased number of paired divalent iron ions and tetravalent titanium ions. The lessened absorption by iron ions resulted in smaller contributions to the color of the gemstone in the yellow to orange spectral range. Increased trivalent chromium ion concentration resulted in increased absorption of the blue and yellow spectral range and increased transmission in the red spectral range. Increased absorption in the yellow-orange range, due to increased absorption by paired divalent iron and tetravalent titanium ions resulted in increased transmission in the blue spectral range. The lessened transmission in the yellow-orange and increase transmission in the red and blue color ranges resulted in the cherry-pink color of the gemstone.

Figure 16. Ranges of colors in sapphires obtained with heat treatment under reducing conditions, within two temperature ranges.
Figure 17. Samples of sapphires before and after heat treatments at 1100-1700 
Degrees C. Samples before treatment are shown in the top row and after treatment shown in the following rows.
Figure 18. Changes in light absorption and transmission in a sapphire with a red-orange color before treatment and a cherry-pink color achieved after treatment.

GALLERY OF SAPPHIRE AND RUBY SPECIMENS

Many specimens on display are from alluvial deposits where erosion of the edges and faces arose from wear against surrounding gravel and sand.

Ref 1. https://www.mindat.org/min-1136.html

Ref 2. http://www.matweb.com/search/datasheet_print.aspx?matguid=c8c56ad547ae4cfabad15977bfb537f1

Ref 3.

https://refractiveindex.info/?shelf=3d&book=crystals&page=diamond

Ref 4. https://en.wikipedia.org/wiki/Asterism_(gemology)

Ref 5.

https://www.researchgate.net/publication/273531857_The_Color_Change_of_Natural_Green_Sapphires_by_Heat_Treatment/download

Ref 6.

https://www.degruyter.com/downloadpdf/j/adms.2012.12.issue-2/v10077-012-0006-3/v10077-012-0006-3.pdf

FIGURE REFERENCES

Fig 1. https://www.gia.edu/gia-gem-corundum

Fig  2.

https://commons.wikimedia.org/wiki/File:Quartz_trigonal_crystal_system_showing_four_axes,_a1_%3D_a2_%3D_a3_%E2%89%A0_c..pdf

Fig 3. http://www.orgoneproducts.eu/crystalsystem/trigonal

Fig 4. http://fredmhaynes.com/2016/06/20/july-birthstone-ruby/

Fig 5. https://m.minerals.net/RoughImage/8/25/Ruby.aspx

Fig 6. https://picclick.com/228-Gram-Natural-Ruby-Gemstone-Cab-Cabochon-Carving-372123410110.html

Fig 7.  http://m.palaminerals.com/prilep/

Fig 8. https://www.crystalarium.com/yellow-sapphire-10-gram-1-54-inch-natural-gem-bipyramidal-crystal-sri-lanka.html

Fig 9. https://www.healingcrystals.com/Ruby_-_Ruby_Tabular_Long_Thin___thick_Crystals__Tanzania_.html

Fig 10. http://www.galleries.com/minerals/gemstone/sapphire/sap-11.jpg

Fig 11. https://www.pinterest.com/pin/239394536426945288

Fig 12. https://www.irocks.com/minerals/specimen/45730

Fig 13..  https://www.irocks.com/search?mode=quick&_token=7jNhAkPkfnqEbdEtH9CcBuNzleQUkvCY0myORXb2&query=corundum

Fig 14. https://www.gemsociety.org/article/how-gems-are-identified/

Fig 15.  

https://www.google.com/search?q=crystal+structure+of+corundum&hl=en&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi25riz3rvfAhUCLqwKHVb7DiMQ_AUIDigB&biw=1307&bih=868#imgrc=4Mgsgr9WFGVmeM:

Fig16-18. https://www.degruyter.com/downloadpdf/j/adms.2012.12.issue-2/v10077-012-0006-3/v10077-012-0006-3.pdf

Figure 19.

https://www.google.com/search?q=sapphire+crystals+yogo+gulch+montana&hl=en&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiHmdaL5PzeAhUPKKwKHXSOCLEQ_AUIDigB&biw=1476&bih=930#imgrc=j1lEOC9zjGdpdM:

Fig 20. https://www.mindat.org/photo-7589.html

Fig 21. https://www.spiriferminerals.com/index.php?static=127

Fig 22. http://www.atggems.com/Photos_Mineral1.htm

Fig 23. 

http://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=39563

Fig 24. https://www.pinterest.com/pin/838443655598552166/

Fig 25.

http://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=14016

Fig 26. https://www.irocks.com/minerals/specimen/42723

Fig 27. http://www.palagems.com/gem-spectrum-v1-n2/

http://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=37057

Beryl Art Objects

In this blog beautiful art objects, carved and sculpted in crystals of the beryl gemstones, are presented. In some, the shape of the gemstone inspired the shape of the object. In others, the color of the object is enhanced by decorating with differently-colored gems. Ancient to modern art objects are presented.

REFERENCES

Ref 1. https://www.metmuseum.org/toah/works-of-art/25.78.90/

Ref 2. https://naomisarna.com/gemstone-carvings-objets-dart/

Ref 3. https://www.britishmuseum.org/research/collection_online/collection_object_details.aspx?objectId=34346&partId=1&searchText=filippo+rega&page=2

Ref 4. https://www.pinterest.com/pin/385128205627297153/

Ref 5. http://www.gemartcenter.com/gemsculptures5.htm

Ref 6. https://www.invaluable.com/auction-lot/an-important-beryl-jewellery-tin-with-diamonds-an-108-c-5804dbd859#

Ref 7. http://www.giabbs.com/post/3473906

Ref 8. https://www.pinterest.com/pin/467248530077414469/

Ref 9. https://www.pinterest.com/pin/576108977315736834/

Ref10. https://www.gemrockauctions.com/auctions/certified-2665-carat-utah-bixbite-carving-729730

Ref 11. https://www.skinnerinc.com/auctions/2843B/lots/325

Ref 12. https://www.christies.com/lotfinder/Lot/a-nephrite-and-morganite-buddha-by-lombard-5620036-details.aspx

Reef 13. https://www.christies.com/lotfinder/Lot/a-unusual-carved-green-beryl-snuff-bottle-5418046-details.aspx

Ref 14. https://www.pinterest.com/pin/342555115386696594/

Ref 15. https://the-gem-hunters.myshopify.com/products/87-ct-morganite-carving-uli-pauly

THE MINERAL BERYL, A MULTIPLEX OF GEMS

The beautiful blue hues of aquamarine, the rich yellows of heliodor, the deep green of emerald, the subtle pinks of morganite, the deep blue of the maxixe beryl, and the rich color of the red beryl (bixbite) span the rainbow, as shown in Figures 1 and 2. The beauty of these gemstones underlies their use by artisans in the crafting of jewelry and art objects, and it’s importance to collectors. 

In this blog, I’ll describe Beryl’s crystal structure and the structural defects and chemical impurities which are the sources of color and fluorescence in beryl. I will also present a summary of sources for beryl gemstones and a photo gallery of mineral specimens from around the world, which I found to be not only aesthetic, but representative of the crystal habits of beryl and demonstrated the color variations and fluorescence in beryl gems. 

Figure 1. Cut gemstones of Aquamarine, Morganite, Heliodor, Maxixe, Goshenite, Red Beryl, and emerald [Ref 1].
Figure 2. Crystals of Aquamarine, Heliodor, Morganite, Emerald, and Red Beryl [Ref 1].

COLORS OF BERYL

Beryl is a beryllium aluminum silicate with the formula BE3Al2(Si6O18) [Ref 2].

Substitution of other metals as impurities for the intrinsic beryllium and aluminum in the crystal lattice of beryl, are the causes of color in beryl. The positions of beryllium, silicon and aluminum ions in the crystal lattice of beryl are shown in Figure 3 [Ref 3]. The divalent beryllium ion (Be2+) is in coordination with four neighboring oxygen atoms, (tetrahedral coordination), and the aluminum ion (Al3+)in coordination with eight oxygen ions, (octahedral coordination). Twelve silicate tetrahedrons are arranged in circular patterns forming rings. The vertical stacking of the 2-D lattice shown in Figures 3.a results in a stacked ring arrangement which forms channels, as shown in Figure 3.b. Water molecules and alkali metal ions, like the monovalent sodium ion Na1+ are located in the channels [Ref 4].

The impurity metal ions and free radical anion responsible for the colors of beryl gemstones are presented in Table I. The process resulting in the absorption of light is electron transfer from a neighboring oxygen to the metal ion. The absorption of light, in regions of the visible light spectrum, defines other wavelengths of the spectrum where the absorption is small and is transmitted or reflected. As an example, the absorption spectrum of heliodor, the golden beryl, taken in polarized light and shown in Figure 4, show a wide absorption peak at ~810 nm in the near infrared part of the spectrum and the ascending flank of a rising peak at a wavelength less than 300 nm in the ultraviolet. Comparison of the wavelength region with low absorption of light, with the colors of the visible spectrum displayed in Figure 5, show the transmitted or reflected light to fall in the yellow-orange range of the spectrum.

Figure 3. Crystal structure of beryl [Ref 3]

TABLE I Impurity Ions and Associated Colors in Beryl[Ref 4,Ref 5,Ref 6]

Cr3+ = trivalent ion of chromium,
Al3+ = trivalent ion of aluminum,
V3+ = trivalent vanadium ion,
Fe2+ = divalent ion of iron,
Fe3+ = trivalent ion of iron,
Be2+ = divalent ion of beryllium,
Mn2+ = divalent ion of manganese,
Mn3+ = trivalent ion of manganese,
NO31- = nitrate radical ion,
CO31- = carbonate radical ion

Figure 4. The absorption spectrum of Heliodor, the golden beryl. The solid and dotted traces represent absorbance values obtained using polarized light vibrating in two perpendicular planes. The net absorption is the sum of the two values [Ref 5].
Figure 5. The visible light spectrum.

FLUORESCENCE OF BERYL

All metal impurity ions listed in Table I fluoresce upon UV light absorption, and serve as activators of fluorescence in beryl. Colors of fluorescence which have been observed in beryl with excitation by a UV lamp are shown in Figure 6 [Ref 6]. Emeralds also exhibit red fluorescence as shown in Figure 4, but require the intensity of laser light for visible fluorescence to be observed. [Ref 7, Ref 8]. The reason for the requirement of intense light for activation stems from the effects of the surrounding lattice about the chromium ion Cr2+ which increases the energy density, (intensity), of light required to excite the electron transitions responsible for fluorescence. A UV lamp is sufficient to excite the chromium ion in ruby because the effect of the lattice on the electrons of the ion is less in ruby.

Figure 6. Fluorescence colors observed in beryl [Ref 5].
Figure 7. Emerald fluorescence spectrum showing activation with 405nm blue light resulting in red and green fluorescence. The red and green fluorescence stems from the chromium and, perhaps iron ions. [Ref 7].

GALLERY OF FLUORESCENT BERYL SPECIMENS

Figure 8. Blue fluorescence of goshenite (colorless beryl) from the Pinwu Beryl mine, Sichuan Province [Ref 9].
Figure 9. Orange fluorescence of beryl from the Ruggles Mine, in New Hampshire under short wave UV illumination [Ref 10].
Figure 10. Red fluorescence of the emerald from the Muzo District, Colombia shown in Figure 9. A 405nm laser was used to illuminate the specimen [Ref 11].
Figure 11. Emerald used for Figure 8 [Ref 12].

SOURCES OF BERYL GEMS

Sources of gem varieties of beryl extend around the world and are summarized in Tables II and III. Many sources of gem-beryl crystals are a cavity in a 

Pegmatite [Ref 5] located within granite [Ref 6]. Others are located in rocks associated with pegmatites. Red beryl is found in the extrusive igneous rock rhyolite. Differently, the emeralds are found in veins of calcite in shale in the mines at Muzo, Colombia. Worldwide locations are summarized in Tables II and III.

Sources of Emeralds [Ref 14]
Sources of Beryl Gemstones [Ref 13]

GALLERY OF GEM BERYL

The specimens shown in Figures 6-18 were selected to demonstrate the variations in the forms of gem beryl crystal and the variations in the characteristic colors of gem beryl. The crystal forms range from a hexagonal prism terminated by a flat face as in Figures 6-11, to prisms terminated by one or more families or pyramidal faces as in Figures 12-18, and to crystals exhibiting higher order prismatic faces as in Figure 11.

Figure 12. Aquamarine with schorl, the black tourmaline, Erongo mountains, Erongo Region, Namibia [Ref 15].
Figure 13. Red Beryl on rhyolite matrix, Violet Mine Wah wah Mountains, Beaver County, Utah [Ref 16].
Figure 14. Heliodor with intense golden color, Capelinha [Ref 17].
Figure 15. Multicolored aquamarine from Nyat, Braldu Valley, Baltistan, Pakistan [Ref18]. The green region stems from the presence the yellow color of an internal core of helidor, adding to the blue of the aquamarine. The flat termination has been eroded in situ. 
Figure 16. Emerald crystals on quartz matrix, Kagem Mine, Kafubu Area, Zambia. The crystals were broken by rock movement and subsequently cemented together by the quartz as seen by the thin white regions long the length of a crystal [Ref 19].
Figure 17. Multicolored pale aquamarine with zones of morganite, Baha, Braldu Valley, Baltistan, Northern Areas, Pakistan [Ref 20]. The striations represent multiple higher order prism faces superimposed on the basic hexagonal prism.
Figure 18. Crystals of aquamarine and heliodor with both complex pyramidal terminations, Minas Gerais, Brazil [Ref 21].

Figure 13. Morganite on feldspar, Chapa Dara District, Konar Province, Afghanistan [Ref 22]. Six narrow pyramidal faces truncate the flat termination of the tabular crystal. The peach tone of the crystals stems from the presence of the ferric ion Fe3+ which imparts the golden color of heliodor to the pink coloration of morganite as seen in Figure18.

Figure 13. Morganite on feldspar, Chapa Dara District, Konar Province, Afghanistan [Ref 22]. Six narrow pyramidal faces truncate the flat termination of the tabular crystal. The peach tone of the crystals stems from the presence of the ferric ion Fe3+ which imparts the golden color of heliodor to the pink coloration of morganite as seen in Figure18.
Figure 14. Multicolored heliodor crystal with pyramidal forms modifying the flat termination and with regions of aquamarine coloration, Befotaka District, Madagascar [Ref 23].

Figure 15. Aquamarine crystal with pyramidal forms modifying the flat termination [Ref 24]. The slight green tone of the crystal stems from the presence of the ferric ion Fe3+.
Figure16. Emerald crystal on carbonaceous calcite, Cincho mine, Mun. de Muzo, Boyac’a Department, Colombia [Ref 25]. Two families of pyramidal faces modify the flat termination of the crystal.
Figure 17. Morganite on albite, Urucum mine, Galileia, Minas Gerais, Brazil [Ref 26]. The termination features stepped growth with a pyramidal face modifying the edge of each step.
Figure 18. Bicolored aquamarine with morganite, Skurdu, Baltistan, Northern Areas, Pakistan [Ref 27].

REFERENCES

Ref 1. https://www.gia.edu/gia-gem-project-beryl

Ref 2. https://www.mindat.org/min-819.html

Ref 3. https://www.researchgate.net/publication/310443635_Dissolution_behaviour_of_beryl

Ref 4. https://link.springer.com/article/10.1007/s00269-008-0228-4

Ref 5. http://www.minsocam.org/ammin/AM53/AM53_777.pdf

Ref 6. https://www.fluomin.org/uk/fiche.php?id=237

Ref 7. Slide 18 in PPT

Investigation of Gem Materials using 405nm Laser Spectroscopy.pptx

Ref 8. https://www.researchgate.net/publication/235471211_Origin_of_the_different_color_of_ruby_and_emerald

Ref 9.

https://www.worthpoint.com/worthopedia/bb-goshenite-ultra-fluorescent-beryl-1468637379

Ref 10. http://tozourfluorescentrocks.net/2d/Page16RugglesMine/BerylmatrixRugglesMineGraftonNH2SW.html

Ref 11. https://www.fluomin.org/uk/fiche.php?id=803

Ref 12. https://geology.com/rocks/pegmatite.shtml

Ref 13. https://geology.com/rocks/granite.shtml

Ref 14. http://www.geo.utexas.edu/courses/347k/redesign/Gem_Notes/Beryl/beryl_triple_frame.htm

Ref 15. https://www.irocks.com/minerals/specimen/8277

Ref 16. https://www.irocks.com/minerals/specimen/41903

Ref 17. http://www.mineralmasterpiece.com/Sold_Specimen_p3.html

Ref 18. https://www.pinterest.com/pin/323203710752245026/

Ref 19. https://collectorsedge.com/pages/the-kagem-emerald-mine-kafubu-area-zambia

Ref 20. http://www.johnbetts-fineminerals.com/jhbnyc/gifs/72325.htm

Ref 21. https://www.mindat.org/photo-144867.html

Ref 22. https://www.mindat.org/photo-231277.html

Ref 23. https://www.mineral-forum.com/message-board/viewtopic.php?p=52056

Ref 24. http://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=48048

Ref 25. https://www.saphiraminerals.com/Search?page=6&updateId=10

Ref 26. http://www.mineralmasterpiece.com/Sold_Specimen_p14.html

Ref 27. https://www.irocks.com/minerals/specimen/43056