Chrysocolla
Chrysocolla is a copper silicate of the oxidised zone, hardness 2 to 4 and density 1.93 to 2.4 — the widest density range of any species this site covers.
Chrysocolla is a hydrated copper silicate of the oxidised zone, hardness about 2 to 4, with a measured density of 1.93 to 2.4 — the widest range of any species this site covers. The Handbook of Mineralogy gives its crystal system as orthorhombic with a question mark, its point group as not determined, and the IMA list records no country of first description.
In short
- Chrysocolla is the worst-characterised mineral most collections contain. The Handbook of Mineralogy prints its crystal system as Orthorhombic (?) and its point group as n.d. — not determined. The IMA list gives its country of first description as unknown and its original reference as a question mark.
- Density runs 1.93 to 2.4, and that spread is the species, not sloppy measurement. The formula ends in ·nH2O with no fixed n, so the water content — and therefore the density — genuinely varies from specimen to specimen.
- Hardness is quoted as about 2 to 4, again a range rather than a value, because what you are testing is usually a cryptocrystalline crust rather than a crystal. Acicular crystals reach only 5 mm.
- Gem silica is not chrysocolla. It is chalcedony — quartz, hardness 7, density 2.65 — coloured by chrysocolla. A steel point settles it in one stroke, because nothing at hardness 2 to 4 resists steel and quartz always does.
- The blue-green copper crusts are separated by density, not by colour. Shattuckite sits at 4.11 and malachite at 4.05, roughly twice chrysocolla. A blue crust that feels heavy in the hand is not chrysocolla.
| Species | Formula | Hardness | Density | What actually separates it |
|---|---|---|---|---|
| Chrysocolla | (Cu,Al)2H2Si2O5(OH)4·nH2O | About 2 to 4 | 1.93 to 2.4 | — |
| Shattuckite | Cu5(SiO3)4(OH)2 | About 3.5 | 4.11 | Nearly twice the density; deep blue, silky |
| Plancheite | Cu8(Si4O11)2(OH)4·H2O | 6 | 3.65 to 3.80 | Hardness 6 — it will scratch glass |
| Malachite | Cu2(CO3)(OH)2 | 3.5 to 4 | 4.05 | Effervesces in dilute acid; pale green streak |
| Turquoise | CuAl6(PO4)4(OH)8(H2O)4 | 5 to 6 | 2.86 | Takes a steel point poorly; a phosphate, not a silicate |
| Chrysocolla chalcedony | SiO2 with chrysocolla colouring | 7 | 2.65 | It is quartz. Scratches steel and glass alike |
What the standard references do not know about chrysocolla
Most species pages on this site begin with a formula and a set of measured constants. Chrysocolla is the one where the references themselves hedge, and it is worth reading what they actually print.
The Handbook of Mineralogy sheet gives the crystal system as Orthorhombic (?), with the question mark in the original, and the point group as n.d. — not determined. The IMA-CNMNC master list for September 2026 carries chrysocolla as an approved species under a 1980 special procedure, gives the formula as (Cu2-xAlx)H2-xSi2O5(OH)4·nH2O — two variables, x and n — and records the country of first description as unknown and the original reference as “original paper?”.
That is not an oversight. It is the honest state of the mineralogy. Chrysocolla is usually cryptocrystalline, often gel-like in origin, and variably hydrated, so the measurements that pin down an ordinary species do not converge. Every other species in our species notes has a type locality; this one does not.
The practical consequence for a collector is narrow and useful: an analytical certificate for chrysocolla can tell you less than one for almost anything else, and a label that names a precise variety of it is claiming more than the reference literature supports.
The density range is the identification, not an obstacle to it
A measured density of 1.93 to 2.4 is the widest range on any Handbook sheet in the set this site covers. Fluorite is 3.18. Calcite is 2.7102. Halite is 2.168. Those are values; chrysocolla's is an interval nearly half a unit wide.
The reason is in the formula. It terminates in ·nH2O, and n is not fixed. More water means a lighter, softer, more porous material; less water means a denser, harder, more compact one. The same specimen can drift within that range as it dries.
Used the right way round, this is diagnostic rather than frustrating. Every blue-green copper mineral chrysocolla is mistaken for is substantially denser: malachite 4.05, shattuckite 4.11, plancheite 3.65 to 3.80. Chrysocolla is the only one of the group that feels too light for its bulk, and a hydrostatic weighing — the method is set out in our note on measuring specific gravity at home — separates it from all of them without ambiguity, where colour separates it from none of them.
Gem silica is quartz, and hardness says so in one stroke
The material sold as gem silica, chrysocolla chalcedony or chrysocolla-in-quartz is chalcedony coloured by included chrysocolla. The species is quartz: hardness 7, density 2.65.
This matters because the two behave nothing alike. Chrysocolla at hardness 2 to 4 is marked by a steel point, abraded by ordinary handling and damaged by ultrasonic cleaning. Chrysocolla-coloured chalcedony is harder than any steel you own and takes a polish that chrysocolla cannot.
One test settles it. A steel needle drawn across an inconspicuous edge either bites or slides. If it slides, the specimen is quartz and the chrysocolla in it is a colouring agent. Our note on testing hardness properly covers doing that without leaving a mark you regret; the short version is to wipe the track and check whether you cut the stone or merely left steel on it.
Where it comes from, and a coincidence worth knowing
Chrysocolla forms in the oxidised portions of many copper deposits and is genuinely worldwide. The Handbook names Katanga in the Congo — the Star of the Congo mine, Likasi and Kakanda — Nizhni Tagil in the Urals, the Timna mine in Israel, Chuquicamata and the Exotica deposit in Chile, Cananea in Sonora, and the Arizona copper districts around Globe-Miami, Morenci, Ray and San Manuel, where it makes up parts of large orebodies rather than mere crusts.
The first locality on the list is the one worth noticing. Lʹubietová near Banská Bystrica in Slovakia — Libethen, in the older literature — appears on the chrysocolla sheet and is also the type locality of libethenite, published from the same place in 1823. An old label reading “Libethen” could reasonably carry either, and the two occur together in the same oxidised copper zone.
We are not a catalogue and hold no stock list. If you have Katangan or Cornish chrysocolla with a legible old label, our wanted list sets out the material and the provenance we are looking for.