PHYSICAL PROPERTIES:
Chemistry: CuSiO3
-H2O
Composition: Hydrated copper silicate
Class: Silicates
Subclass: Cyclosilicates
Crystal system: trigonal
Fracture: conchoidal and brittle
Hardness: 5
Specific gravity: 3.3
Refractive Index: 1.65 - 1.71
Luster: vitreous
Streak: green
Cleavage: perfect in three directions
Color: deep green
Transparency: transparent to translucent
Associated Minerals: Many of the
copper minerals along with dolomite, calcite, cerussite, wulfenite and
limonite.
COMPOSITION:
Hydrous silicate of copper (50.4% CuO, 38.2% Si02,
11.4% H20)
DISTINGUISHING CHARACTERISTICS:
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
ENVIRONMENT:
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.
CRYSTAL DESCRIPTION:
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.
TESTS:
Crystals dull in hydrochloric acid; decapitate, blacken, and give
water in closed tube; turn brown on charcoal, without fusing.
LOCALITIES:
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.
USES:
Mostly as mineral specimens, rarely as gemstones 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.
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