Dioptase

Dioptase

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

1
Talc 2
Gypsum 3
Calcite 4
Fluorite 5
Apatite 6
Orthoclase 7
Quartz 8
Topaz 9
Corundum 10
Diamond

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.

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

The name Dioptase has a specific etymological and historical context — see Mindat's reference entry for provenance details. We have retained naming data at the record level; published prose is paraphrased from factual fields rather than copied from source.