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Formula: CuSiO3.H2O
Cyclosilicate (ring silicate)
Crystal System: Trigonal
Specific gravity: 3.28 to 3.35 measured, 3.296 calculated
Hardness: 5
Streak: Green
Colour: Emerald green
Solubility: Moderately soluble in hydrochloric acid
Environments:
Dioptase occurs as a secondary mineral in the oxidised zone
of high temperature hydrothermal copper deposits (Webmin, HOM).
Associated minerals include chrysocolla,
malachite, mimetite,
wulfenite, cerussite,
hemimorphite, fluorite and
quartz
(HOM, Mindat).
Localities
At the type locality, the Altyn-Tyube dioptase deposit, Bukhar-Zhyrau, Karaganda Region, Kazakhstan, dioptase
occurs as a secondary mineral in the oxidised zones of
copper deposits
(Mindat).
Altyn-Tyube was mined for copper in the bronze age, and dioptase has been
known from there since Roman times, but originally it was thought to be emerald.
Well over a thousand years later, towards the end of the eighteenth century, mineralogists began to doubt the
identification, and after a bit of argument the name "dioptase" was settled on. The area is remote, poorly mapped and
difficult of access, but over the years intrepid mineral collectors have reached it and been rewarded by beautiful
specimens.
The limestone at Altyn-Tyube is cut by numerous fissures lined with
calcite and dioptase; copper
mineralisation is genetically associated with a nearby andesite
porphyry intrusion. Hydrothermal alteration deposited
quartz, carbonates, baryte and
anhydrite in the limestones,
and iron-magnesium rich hydrothermal alteration produced a fine-grained
epidote-chlorite bearing assemblage in
the volcanic rocks.
The primary ore minerals at
Altyn-Tyube were chalcopyrite,
bornite, pyrite and
chalcocite, with rare galena and
sphalerite.
Among the secondary minerals, dioptase is the most
pronounced, forming beautiful crystals in cavities in hard, silicified
limestones. They are occasionally accompanied by sheaf-like
malachite aggregates and colourless, scalenohedral
calcite crystals. Other
secondary minerals include
chrysocolla, azurite,
tenorite, pseudomalachite,
cuprite and native copper.
Dioptase at Altyn-Tyube forms attractive specimens, with sharp green crystals, sometimes up to 3 cm in size, in
thick blankets over a characteristic white to brownish veined limestone
(MinRec 54.2.209-253).
At the Pool Department, Republic of the Congo, dioptase has been found in good quality and various forms.
Single large crystals, crystal clusters and small crystals with
perimorphs of an unknown mineral, or specimens in small pockets are
found.
Associated minerals include mimetite,
plancheite and quartz
(Dr Marco Tam Shing Yau, The Mineralogy Society of Hong Kong Newsletter 19.8).
At the Magma mine, Pioneer District, Pinal county, Arizona, USA, dioptase has been found associated with minor
amounts of chrysocolla, azurite,
malachite and olivenite, and
occasionally crystals of wulfenite and
cerussite to 2 mm
(R&M 95.1.84).
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