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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).
Dioptase from Altyn-Tyube - Image
At the Tsumeb Mine (Ongopolo Mine), Tsumeb, Oshikoto Region, Namibia, fine specimens of dark green dioptase
have been found
(Mindat photo).
Dioptase from Tsumeb - Image
At the Renéville Mine, Renéville, Kindanba District, Pool Department, Republic of the Congo, dioptase is
found as crystalline masses and geodes, some of which can reach 50 cm in their longest dimension. The individual
crystals, sometimes doubly terminated, rarely exceed 3 or 4 cm. They occur associated with many minerals including
plancheite, cerussite,
cuprite, mottramite,
fornacite, chrysocolla,
azurite, malachite,
wulfenite, pyromorphite,
chalcocite, quartz and
calcite.
In general, dioptase crystals from Renéville occur in vugs in massive dioptase lenses, the vugs
commonly lined by baby-blue chrysocolla. The dioptase crystals
are bright green, but sometimes with a mottled appearance because of cloudy inclusions, and lack the uniform very
dark green tones of Tsumeb dioptase
(MinRec 55.4.425-433).
Dioptase from Renéville - Image
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).
Dioptase from the Magma Mine - Image
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