silicates
Chrysocolla
(Cu2-xAlx)H2-xSi2O5(OH)4·nH2O
- Also known as
- gem silicaeilat stone
- Crystal system
- orthorhombic
- Hardness
- 2–4 on the Mohs scale
- Lustre
- vitreous
- Colour
- Blue-green to cyan
- Where it forms
- In the oxidised zones of copper deposits, often as a crust or as a filling between other minerals rather than as crystals.
- Chiefly from
- PeruDemocratic Republic of the CongoArizona, United StatesIsrael
Why it is that colour
Copper, in a hydrated copper silicate. The very bright blue-green is distinctive and hard to mistake for anything else in the field.
Safety
A copper mineral, and very soft — often softer than a fingernail in its pure form. Do not put it in water or in your mouth. The harder material sold as gem silica is chrysocolla-coloured chalcedony and is chemically far more stable.
Where it comes from
Peruvian and Congolese material is common. Israeli eilat stone from Timna is mostly exhausted and much of what is sold under the name is imported material or an imitation.
Historical use
Used as a soldering flux in antiquity, which is where the name comes from, and as a minor pigment. Never a major gem because it is too soft to hold a polish unless it has been silicified.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
The Greek name means gold glue, because it was used as a flux in soldering gold. Eilat stone, a mixture of chrysocolla with malachite and turquoise from the Timna valley, is marketed as King Solomon’s stone, a connection which is geographical rather than documented. Modern meanings are recent.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Sold as this, but not
Worth knowing
Chrysocolla presents a small classification headache that is worth knowing about. Much of the finest material is not really chrysocolla at all: it is chalcedony that has been coloured by chrysocolla inclusions, sold as "gem silica" and priced accordingly. That material is quartz, hardness 7, and takes a superb polish. Pure chrysocolla is a soft crumbly crust that will not survive being worn.
Two things sold as the same stone, differing by a factor of a thousand in durability, and the difference is which mineral is doing the structural work.
Identity checked against IMA-CNMNC master list, June 2025.