Gem library
Chrysocolla
Copper blue-green, in velvety crusts
Chrysocolla is a hydrated copper silicate of a luminous blue-green, often in velvety botryoidal crusts. Extremely soft when pure, it becomes a remarkable gem when silica has impregnated it: that is gem silica, the most expensive of the chalcedonies.
- Hardness (Mohs)
- 2.5 – 3.5 (up to 7 if silicified)
- Density
- 1.90 – 2.45
- Crystal system
- Amorphous to cryptocrystalline
- Refractive index
- 1.575 – 1.635
- Cleavage
- None
Mineralogical identity
- Family
- Hydrated copper silicates
- Species
- Chrysocolla
- Variety
- Chrysocolla in chalcedony (gem silica), Eilat stone
- Chemical formula
- (Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O
- Crystal system
- Amorphous to cryptocrystalline (orthorhombic)
- Classification
- Collector's mineral · ornamental stone
- Rarity
- Uncommon
- Indicative price
- €0.50 – 60/ct (gem silica: up to €200/ct)
Etymology
From the Greek khrusos, gold, and kolla, glue: it is the name Theophrastus gave to a material used as a flux for soldering gold.
Physical & optical properties
- Hardness (Mohs)
- 2.5 – 3.5 (up to 7 if silicified)
- Density
- 1.90 – 2.45
- Refractive index
- 1.575 – 1.635
- Birefringence
- 0.023 – 0.040
- Cleavage
- None
- Fracture
- Conchoidal to irregular
- Lustre
- Vitreous to earthy
- Diaphaneity
- Translucent to opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- blue-green, turquoise, sky blue
Formation, geology & history
A variable, unstable composition
Chrysocolla is poorly defined mineralogically: its formula fluctuates, its structure is amorphous to cryptocrystalline, and its water content varies greatly. It forms in the oxidation zone of copper deposits, alongside malachite, azurite and cuprite, as mammillated crusts, coatings and fracture fills. In its pure state its hardness can drop to 2: it crumbles under a fingernail and cannot be polished. That is why ornamental material is almost always a mixture — chrysocolla impregnated with quartz, chalcedony or opal, which raises the hardness to 5, 6 or even 7.
Gem silica, the priciest chalcedony
When chrysocolla is intimately mixed with chalcedony, the result is a translucent material of intense blue-green, hard and mirror-polishable: gem silica, also called chrysocolla chalcedony or blue chrysoprase. The finest specimens, from the Arizona mines, reach €200 a carat, making it by far the most precious of the chalcedony varieties — dearer than green chrysoprase. It is recognised by its translucency and vitreous lustre, very different from the earthy velvet of pure chrysocolla. A sought-after variant is the «bouquet» combining blue chrysocolla, green malachite and red cuprite in a single piece.
Eilat stone and copper cultures
In Israel, the ancient copper mines of Timna, worked since the Bronze Age and traditionally associated with King Solomon, produce Eilat stone: a natural mixture of chrysocolla, malachite and turquoise in blue-green marbling, which became Israel's national stone. The deposit is now exhausted and material sold under that name often comes from elsewhere. More broadly, chrysocolla has served as a pigment and a prospecting indicator: its presence at the surface signals a copper deposit, and its Greek name recalls its ancient use as a brazing flux for gold.
How to recognise it
- Luminous, velvety blue-greenPure chrysocolla has a characteristic matt, silky look in mammillated crusts. Gem silica, by contrast, is translucent and glossy.
- Very soft when pureIt is scratched by a fingernail or a needle. If your blue-green stone scratches glass, it is silicified gem silica, not pure chrysocolla.
- LightnessDensity 1.9 to 2.45: very light, including compared with turquoise (2.7). A clear clue against heavier imitations.
Imitations, treatments & confusions
- Dyed howlite or magnesiteChalky appearance, regular black veins, dye that bleeds with acetone. Very common in beads sold as chrysocolla.
- Resin and reconstituted powderOver-regular patterns, lightness suspect even for chrysocolla, plastic smell on a hot point.
- Confusion with turquoise and amazoniteTurquoise is harder and matt with a brown matrix; amazonite has pearly cleavage planes. Chrysocolla is softer and lighter than both.
Deposits & origins
Democratic Republic of Congo (Katanga), Peru (Lily mine), United States (Arizona: Ray, Inspiration; gem silica from the Keweenaw deposit), Chile, Mexico, Israel (Timna, the Eilat stone combining chrysocolla, malachite and turquoise), Russia
Care & precautions
- Never water: it is a hydrated copper silicate, very sensitive to moisture and acids. The polish dulls and the material can delaminate.
- A soft dry cloth only. No household products, no solvents.
- Extremely fragile when pure (hardness 2-3): individual storage, careful handling. Gem silica, being hard, is by contrast robust.
- No ultrasonic cleaning or steam. Most commercial cabochons are resin-stabilised: in that case avoid heat too.
Traditions & crystal healing
- Chakras
- Throat · heart
- Zodiac signs
- Gemini · Taurus
- Element
- Water · Air
Tradition makes it a stone of calmed speech and quiet wisdom, associated with the throat and the heart. It is credited with a mediating role, helping express difficult truths gently. Its water blue-green and its link to copper connect it symbolically with Venus.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Chrysocolla or turquoise?
Chrysocolla is softer (2.5-3.5 against 5-6), markedly lighter, and its blue-green more luminous and velvety. Turquoise has an irregular brown or black matrix.
What is gem silica?
Chrysocolla intimately mixed with chalcedony: translucent, hard (up to 7), of an intense blue-green. It is the most precious of the chalcedonies, up to €200/ct.
Can it go in water?
No. It is a hydrated copper silicate, sensitive to water and acids. A dry cloth is the only recommended care, except for silicified gem silica.