Dioptase, 2.16 cts, faceted by AGTA Spectrum Award-winner Mark Kaufman. Christoph Mine, Kaokoveld, Namibia. © Rob Lavinsky, www.iRocks.com. Used with permission.
Dioptase has a beautiful, emerald-like green color. Although this mineral isn’t rare, gems are seldom faceted because of a paucity of clean material over 1 carat.
| Data | Value |
|---|---|
| Name | Dioptase |
| Colors | Rich emerald green, blueish green. |
| Hardness | 5 |
| Fracture | Conchoidal to uneven |
| Cleavage | Perfect 1 direction |
| Formula | CuSiO2(OH)2 |
| Crystallography | Hexagonal (Trigonal). Fine prismatic crystals are common in certain localities; stubby, elongated. |
| Refractive Index | 1.644-1.709 |
| Birefringence | 0.053 |
| Dispersion | 0.036 |
| Luminescence | None |
| Luminescence Present | No |
| Absorption Spectrum | Broad band at about 5500; strong absorption of blue and violet. |
| Pleochroism | Weak: dark emerald green; light emerald green. |
| Optics | o = 1.644-1.658; e = 1.697-1.709. Uniaxial (+). |
| Optic Sign | Uniaxial + |
| Luster | Vitreous |
| Fracture Luster | Greasy |
| Specific Gravity | 3.28-3.35 |
| Transparency | Translucent to transparent. |
| Etymology | From Greek words meaning “to see through,” because the cleavage directions can be determined just by looking into the crystals. |
| Occurrence | Oxidized zone of copper deposits. |
Dioptase crystals on matrix, 73 x 40 mm, Tantara Mine, Katanga, Democratic Republic of the Congo. Photo courtesy of liveauctioneers.com and Marques Dos Santos, Lda.
Dioptases usually occur as micro-crystals. Although larger crystals can be found, they rarely have large clean areas, so any faceted gems rarely weigh more than 1 or 2 carats. Perfect cleavage can also make these gems difficult to facet. However, lapidaries can cut sizable cabochons from translucent dioptase masses.
Dioptase rough and cut set. Rough specimen: 4.5 x 4.2 x 4.0 cm (largest crystal: 1.2 cm); emerald-cut gem: 0.65 cts. Tsumeb Mine, Otjikoto, Namibia. © Rob Lavinsky, www.iRocks.com. Used with permission.
With their beautiful green colors and doubly terminated and often prismatic crystal shapes, dioptases are frequently found in mineral collections. They also make popular freeform and raw jewelry stones.
18k yellow gold earclips with rough dioptase crystals. Photo courtesy of liveauctioneers.com and Henry’s Auktionshaus AG.
Dioptases have a pale blue-green streak. Keep in mind that streak testing is a destructive test. Conduct it only as a last resort for identification and never on a finished gem.
When heated, dioptase generates an electric charge. This property is known as pyroelectricity.
Faceted dioptases may show a birefringent doubling effect.
Dioptases may resemble more well-known gemstones such as emeralds and peridots. Despite their similar colors, the optical and physical properties of dioptases and emeralds differ enough that gemologists can readily distinguish them. On the other hand, dioptases and peridots can have similar refractive indices (RI), pleochroic colors, and specific gravity (SG) values. However, they have distinct absorption spectra and different optic characters. (Dioptases also typically show darker green colors than peridots).
Green tourmalines may share many properties with dioptases. However, dioptase has a distinctive absorption spectrum.
Doubly terminated dioptases on a malachite matrix, Kaokoveld Plateau, Kunene Region, Namibia. © Rob Lavinsky, www.iRocks.com. Used with permission.
A hydrous copper silicate, dioptase has been called “emerald copper” because of its color. Dioptase can form in close association with malachite, another copper-bearing mineral. You may find dioptase specimens sometimes described as “emerald malachite,” perhaps because their crystalline formations appear “gemmy,” like emeralds, and their color is similar to that of more well-known malachites. Of course, dioptase, malachite, and emerald constitute three distinct gem species. This is likely another example of vendors falsely connecting a gemstone — in this case — with not one but two more well-known gemstones in an effort to increase consumer interest (and prices). See our list of false or misleading gemstone names for more examples.
Scientists have synthesized dioptases. However, there is no known jewelry use for this lab-created material.
No known gemstone treatments or enhancements.
Tsumeb, Guchab, and Kaokoveld, Namibia produce the world’s finest crystals, with superb color, on matrix, and up to 2 inches long. Some are transparent but also filled with cleavage planes and fractures.
The dioptase type locality, Altyn-Tyube, Kazakhstan, also produces fine crystals.
This specimen (47 x 43 mm) from Altyn-Tyube, Kazakhstan features many well-formed dioptases. Photo © Joel E. Arem, PhD, FGA. Used with permission.
In the United States, Arizona yields microscopic crystals.
Other notable sources include the following localities:
Dioptase crystals, Cerro Negro Mine, Cerro Negro district, El Salado, Chañaral Province, Atacama Region, Chile. Photo by Leon Hupperichs. Licensed under CC By-SA 3.0.
Large crystals seldom produce gems larger than 2 carats. Masses may yield cabochons up to 15 carats.
Dioptase oval cabochon, 1.56 cts. Photo courtesy of liveauctioneers.com and Pioneer Auction Gallery.
With perfect cleavage and a hardness of 5, dioptases need protective settings whether faceted, cabbed, or raw. These gems have greater susceptibility to scratches than other, more popular jewelry stones like tourmalines, peridots, and even emeralds. However, dioptases make excellent choices for earrings or brooches.
Apatite and dioptase gold-filled wire earrings. Photo courtesy of liveauctioneers.com and Michaan’s Auctions.
Due to its copper content, dioptase dust is toxic. Accidental ingestion could lead to acute distress, like vomiting, and chronic exposure could lead to liver and kidney damage. Faceters should wear protective masks and, ideally, use a glovebox to prevent inhaling or ingesting dioptase particles during cutting, polishing, and cleaning. However, wearing or handling finished pieces should pose no hazards.
Due to cleavage and possible fractures, dioptases should only be cleaned with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more care recommendations.
Faceted dioptase, 0.41 cts. Photo © Joel E. Arem, PhD, FGA. Used with permission.
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