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Dioptase

Curated by Maggie Liu · Updated:

Crystal system · Trigonal

Dioptase is a silicate mineral recognized among collectors for its crystal form and distribution.

Emerald-green dioptase cluster on limonite matrix from Congo, DRC
Hydrous copper silicate, vivid emerald-green; hexagonal/trigonal.

About Dioptaseextended article

Color Cause (Chromophore)
Chromophore:
Cu²⁺
Mechanism:
idiochromatic
Color produced:
emerald green
Among the most intensely green Cu minerals.
Mohs 5
Vickers (~) 540 HV
Knoop (~) 620 HK
Element composition by mass

Formula: CuSiO₃·H₂O · molar mass: 157.64 g/mol

O 40.6%
Cu 40.31%
Si 17.82%
H 1.28%

Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.

Mohs Hardness 5

Dioptase sits at 5 on the Mohs scale — can be scratched by a steel knife.

Colors:
Streak
Green
Crystal system
Trigonal
SilicatesSilicates (Cyclosilicates)
TL;DR · 1 min read
Dioptase (CuSiO₃·H₂O) is a vivid emerald-green copper silicate that ranks among the most visually striking minerals on Earth. Its color rivals gem emerald, and it forms sharp prismatic to rhombohedral crystals in the oxidized cap of copper deposits.

Dioptase (CuSiO₃·H₂O) is a vivid emerald-green copper silicate that ranks among the most visually striking minerals on Earth. Its color rivals gem emerald, and it forms sharp prismatic to rhombohedral crystals in the oxidized cap of copper deposits. Tsumeb (Namibia) and Mindouli/Mfouati (Republic of Congo) produce world-class specimens.

More minerals to explore

About Dioptase

Dioptase is classified as a silicate mineral in the dioptase group and has the chemical formula CuSiO₃·H₂O. It crystallizes in the trigonal system and holds a steady position among silicate species. Its combination of structural character and global distribution make it a recognized species in both systematic and aesthetic collections.

Identification & care

Specimens usually show short prismatic rhombohedral crystals; commonly on matrix. Its color is typically emerald green to blue-green. The luster is sub-adamantine, vitreous, sub-vitreous, the streak is green, and specimens range from transparent to translucent. The cleavage is perfect rhombohedral {1011} in 3 directions. The fracture is conchoidal, which aids identification.

Collector context

How it forms

In terms of geology, Dioptase forms in secondary mineral in oxidized zones of copper ore deposits. It is commonly found in association with wulfenite, malachite, calcite, chrysocolla, shattuckite.

Why collectors care

Dioptase is a frequently-sought species in serious collections because its habit is recognizable, its color often strong, and its best examples unmistakable even at a distance. Chinese material has driven much of the recent visual shift in the species — sharper crystals, deeper colors, cleaner matrix.

What affects value

Value in Dioptase is assessed, in typical order of weight, against: (1) locality provenance; (2) size relative to the species norm; (3) crystal form and termination sharpness; (4) color saturation and zoning; (5) transparency and internal clarity; (6) matrix quality and aesthetic balance; (7) condition (absence of damage, chips, or repair). Cleaning quality and verified locality documentation act as multipliers across the above.

Naming history

Dioptase is Greek for "to see through": dia, through, plus optazein, to see. The name records a moment of mineralogical embarrassment — the first specimens, found in Kazakhstan in the late 18th century, were taken for emerald, and the internal cleavage planes visible through the transparent crystal were what finally gave it away as something else entirely.

Frequently asked questions

What is Dioptase?

Dioptase has the chemical formula CuSiO₃·H₂O, crystallises in the Trigonal system. Dioptase is a silicate mineral recognized among collectors for its crystal form and distribution.

What is the chemical formula of Dioptase?

The chemical formula of Dioptase is CuSiO₃·H₂O.

What crystal system does Dioptase belong to?

Dioptase crystallises in the Trigonal crystal system.

Where is Dioptase found?

Notable localities for Dioptase include Tsumeb.

Related minerals

Available Dioptase specimens

5 specimens
Dioptase emerald-green crystal cluster from Republic of Congo
DR Congo

Dioptase Crystal Cluster, DR Congo

$185.00
Dioptase crystal cluster from Democratic Republic of Congo
DR Congo

Dioptase Crystal Cluster, DR Congo

$195.00
Three dioptase crystal specimens Congo front view
DR Congo

Emerald Dioptase Trio on Tan Matrix, DR Congo

$68.18
Emerald-green dioptase cluster on limonite matrix from Congo, DRC
DR Congo

Dioptase Cluster on Limonite Matrix – DR Congo

$298.00
Sale
Vibrant green dioptase crystals on matrix, Tsumeb Mine, Kaokoveld, Namibia
Namibia

Dioptase Crystal Cluster – Vibrant Green – Tsumeb Mine, Namibia

$216.00 $240.00

Recently sold Dioptase specimens

2 examples — for reference
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Dioptase on matrix from Morocco with vivid emerald-green crystals
Morocco

Dioptase on Matrix, Morocco

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Dioptase crystals on matrix Congo front view
DR Congo

Dioptase Crystal on Matrix – DR Congo

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