The Mineral Dioptase
Chemistry: CuSiO3 -H2O
Composition: Hydrated copper silicate
Crystal system: trigonal
Fracture: conchoidal and brittle
Specific Gravity: 3.3
Refractive Index: 1.65 - 1.71
Color: Teal to Deep Green
Cleavage: perfect in three directions
Transparency: transparent to translucent
Associated Minerals: Many of the copper minerals along with dolomite, calcite, cerussite, wulfenite and limonite.
Hydrous silicate of copper (50.4% CuO, 38.2% Si02, 11.4% H20)
Dioptase is one of the few minerals that comes close to emerald's deep green. However it's good cleavage and softness make it an unlikely candidate for use as gemstones. Although Dioptase is harder than most similar green minerals, the copper sulphates, carbonates, and the phosphates. The rhombohedral termination is invariable and typical. Brochantite reacts on charcoal, is softer, and crushes easily to a green powder. Malachite dissolves in hydrochloric acid with effervescence.
Dioptase is often found in arid climates. It forms in parts of copper veins that have been oxidized by air or water, and in the hollows and cavities that surround this type of rock.
Dioptase is one of the few rhombic silicates. It forms crystals that can have a typical carbonate rhombohedral shape. Like those of the mineral dolomite. The faces of the rhombohedrons, and even the prism faces, are very reflective due to a fairly high luster. Crystals can be quite clear but the deep color may often block the light. Dioptase often forms stubby six sided prisms, that have three faces of a rhombohedon. Long prismatic habits are rare. Simple rhombohedrons are also common. Some times a second rhombohedron will modify the primary rhombohedron faces producing a second set of three smaller faces. Crusts and massive forms are also found.
Crystals dull in hydrochloric acid; decapitate, blacken, and give water in closed tube; turn brown on charcoal, without fusing.
The most famous and original find was in the Ural Mountains. At Altyn-Tube in the Khigiz steppes of Kazakhstan. These specimens are found in seams of limestone, on brownish quartz. Dioptase is also found at Soda Lake Mountain, in Saint Bernardino, California, Rich crusts of very slender, short, upright green needles associated with willemite and wulfenite were found at Tiger, Arizona, in the Mammoth Mine. Because of the similarity to brochantite and malachite, dioptase it is probably more common than is generally realized at many of the western copper mines. Tsumeb, Southwest Africa, is remarkable as the source of the largest dioptase crystals, which may be up to an inch in length. More slender prismatic crystals up to 2 inches long have been found at Mindouli in the French Congo.
Mostly as mineral specimens, sometimes as gemstones especially small druzy plates and a very minor ore of copper.
FACTS & HISTORY:
Dioptase gets its name from the Greek dia ("through") and optos ("visible")
Specimens from Kazakhstan were wrongly identified as emeralds and sent to the court of the Russian Tsar in St. Petersburg. The mistake was not realized until the early nineteenth century.