Quartz is one of the most ubiquitous minerals in the world, though gem-quality material is still rare. Quartz occurs in many forms, but the species can usefully be divided into two families according to structure: the macrocrystalline and the microcrystalline.
Macrocrystalline quartz has larger crystals that can be detected by the naked eye, while microcrystalline varieties are formed from aggregates of tiny crystals that can only be seen under under the microscope.
Macrocrystalline quartz varieties tend to be transparent with a vitreous luster, and include amethyst, ametrine, citrine, rose quartz and rock crystal. The microcrystalline varieties tend to be opaque with a waxy luster, and includes gems like chalcedony, agate, onyx, carnelian, bloodstone, gem silica and chrysoprase.
Chrysoprase is probably the least known member of the microcrystalline group, but it is generally considered to be one the rarest and most valuable. It ranges in color from a soft to vivid apple-green, and especially fine specimens have considerable translucency. It is usually cut as cabochons and makes attractive rings and pendants. It can be found in larger sizes as well.
Like the other microcrystalline quartzes, chrysoprase has a hardness of 6.5-7 on the Mohs scale, a density of 2.58 to 2.64, and refractive index of 1.530 to 1.540.
Natural quartz is colorless and colored specimens get their color from trace elements. Chrysoprase is colored green by nickel and is one of very few gemstones colored by this element (the other is gaspeite). Green gems are typically colored by iron (peridot), chromium (emerald, chrome tourmaline, chrome diopside) or vanadium (tsavorite garnet).
Chrysoprase tends to occur in weathered materials from nickel deposits. The most famous historical chrysoprase deposits were in Poland. Chrysoprase is now found in a number of locations, including Australia, Brazil, Madagascar and Tanzania. The chrysoprase from Central Queensland in Australia is particularly fine and some specimens display the prized translucency that give the impression of high quality jade. Australia now produces about 85% of the world's supply of chrysoprase.
We have recently cut a number of excellent pieces from some particularly fine Australian chrysoprase. This material has very good translucency that produces that wonderful luminosity that makes top grade chrysoprase so special.
See all our Fine Chrysoprase Gems
Notable Gems from the AJS Collection
This month we feature recent acquisitions to our collection.
Click on a photo to see the details for the item.
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11.79 ct Sphalerite from Spain [SOLD]
An outstanding large sphalerite from the Aliva mine in northern Spain. This gorgeous round sphalerite is over 11 carats and is amazingly bright and fiery, with flashes of orange, yellow and green as it is turns in the light. Beautifully cut and very clean, this is a superb gem sphalerite for your collection. Guaranteed natural and untreated. |
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6.66 ct Blue Zircon from Cambodia [SOLD]
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An exquisite peach morganite with wonderful fire. This fine material has been precision-cut in a modified radiant cut and polished to perfection. This gem is sure to please the most discriminating collector and will look stunning when set in your jewelry design. Guaranteed natural and untreated. |
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3.10 ct Fancy Tanzanite from Tanzania [SOLD]
A rare purple tanzanite, completely natural and untreated. This fine gem has a wonderfully pure saturated color and is completely clean even under magnification. Perfectly cut to bring out the fire and brilliance of this excellent material, this 3.10 ct gem will set up beautifully in a ring or pendant. Guaranteed natural and untreated.
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26.06 ct Apatite from Madagascar [SOLD]
An outstanding large (17 mm) round Apatite that looks like a Paraiba Tourmaline that would sell for thousands of dollars per carat. This is a brilliant gemstone cut to ensure excellent shape, polish and brilliance, with full luster, no windows and a fully saturated vivid aqua blue color. This stone is sure to impress in your jewelry design. Guaranteed natural. |
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13.17 ct Chrysoprase from Australia [SOLD]
An outstanding gem chyrsoprase from Australia with a delicious apple-green color and excellent translucency. This gem displays the wonderful luminosity that is characteristic of the very best chrysoprase. Guaranteed completely natural and untreated. |
News from AJS and the Gems World
- 404 carat Flawless Diamond Discovered in Angola
The Lucapa Diamond Company of Australia announced that they have discovered a 404.2 ct rough diamond at the Lulo mine in Angola. The diamond has been analyzed as a rare D-color type IIa stone, meaning it has no chemical impurities whatsoever. It is the largest diamond ever discovered in Angola, more than twice as large as a 217.4 carat diamond discovered in 2007; and is the 27th largest diamond ever discovered in the world.
In a subsequent announcement on February 29th, Lucapa disclosed that they have sold the 404.2 carat diamond for $16 million. The per carat price of $39,580 is the highest price paid to date for a white diamond at the Lulo Diamond Project.
- GIA to offer more than $500k in Scholarships
The Gemological Institute of America (GIA) is offering more than 125 scholarships worth over $500,000 for the institute’s gemology and jewelry manufacturing arts programs, courses and lab classes. Awards range from $500 to $22,000. The GIA has awarded more than $3.5 million in scholarships to almost 1,000 students since 2013. Scholarships are funded by the GIA endowment fund and private donors.
Scholarships are available for distance “eLearning” courses and for classes at GIA’s campuses in Bangkok, Carlsbad, Dubai, Hong Kong, London, Mumbai, New York and Taiwan. Applications open March 1 and run until April 30.
Ask the Gem Experts
Each month we answer questions from our customers. We welcome your questions and you can submit a question from our contact page.
Could you please tell me the difference between ruby and rubellite? Thanks, HL, Singapore.
Despite the similarities in the names, ruby and rubellite are entirely different species. Ruby is the red color of corundum (with non-red corundum known as sapphire) while rubellite is the pinkish-red to violet-red color of tourmaline.
Why do diamonds feel cold to the touch? Is this true of any other gemstone? GW, USA.
One of the oldest tests for the authenticity of a diamond is to touch the stone to your lip and see if it feels cold. Diamond is an exceptional conductor of heat -- better even than metals such as silver, gold and copper.
Really no other natural gemstone has thermal conductivity that can even remotely compare with diamond. Unfortunately the old diamond test of touching the gem to your lip is not reliable, since a synthetic diamond simulant called moissanite has thermal conductivity similar to diamond. Cubic zirconia, on the other hand, conducts heat very poorly and is classified as a thermal insulator.
All the best in gems,
Arnold, Rung & Ron
