Crocoite
Crocoite is PbCrO4, hardness 2.5 to 3, density 6.0 to 6.1, crystals to 15 cm. It is sectile rather than brittle, and its terminations are often hollow.
Crocoite is lead chromate, PbCrO4, monoclinic, hardness 2.5 to 3 with a measured density of 6.0 to 6.1 and crystals to 15 cm. The colour is hyacinth-red to orange, the streak yellow-orange, the lustre adamantine. The Handbook of Mineralogy records that this mineral may be of post-mine formation.
In short
- Crocoite is sectile, not brittle. That single word in the Handbook of Mineralogy explains most of what happens to these specimens in transit: a sectile mineral deforms and shears rather than snapping cleanly, so a crushed crocoite spray does not break along a crystal, it folds.
- Hollow or incomplete terminations are normal. The Handbook states that terminations are commonly hollow or incomplete. A crocoite prism that ends in an open box is not necessarily damaged, and a dealer describing it as undamaged is not necessarily wrong.
- Density 6.0 to 6.1 at hardness 2.5 to 3 is the worst combination a collector can be handed. It is heavy enough that a spray cannot support itself in awkward orientations and soft enough that anything it touches marks it.
- The Dundas district in Tasmania set the standard — the Adelaide, West Comet, Heazlewood, Whyte River and Magnet mines — but the type material came from Beresovsk in the Middle Urals, and Britain has two occurrences of its own.
- Crocoite is a lead chromate and both halves are hazardous. Handle it with gloves, wash afterwards, and never work it dry in a way that generates dust.
| Species | Formula | Hardness | Density | Streak | Habit that separates it |
|---|---|---|---|---|---|
| Crocoite | PbCrO4 | 2.5–3 | 6.0–6.1 | Yellow-orange | Acicular to prismatic, near-square section, striated, radial sprays |
| Wulfenite | PbMoO4 | 2.75–3 | 6.5–7.5 | White | Square tabular plates, not prisms |
| Vanadinite | Pb5(VO4)3Cl | 2.5–3 | 6.88 | White to pale yellow | Hexagonal prisms, often hoppered barrels |
| Realgar | As4S4 | 1.5–2 | 3.56 | Red-orange to red | Much lighter in the hand; degrades in light to a powdery orange |
| Mimetite | Pb5(AsO4)3Cl | 3.5–4 | 7.24 | White | Hexagonal; the Caldbeck campylite form is barrel-shaped |
Why crocoite arrives broken more often than anything else
Four properties combine badly. The habit is acicular to prismatic in radial sprays, so the mechanically weakest possible shape carries the whole specimen. The density is 6.0 to 6.1, which for a needle is a great deal of mass on a thin section. The hardness is 2.5 to 3, below a fingernail in places and well below anything it might rub against. And the tenacity is sectile: it gives way rather than resisting.
The practical consequence is that crocoite must never be packed so that it can move, and never packed so that it is held firmly either. A spray needs to sit in a cavity that supports the matrix and leaves air around every crystal. Our guidance on packing and shipping specimens applies here more than to any other species on this site.
Do not attempt to clean a crocoite. Brushing removes crystals, ultrasonic cleaning removes crystals, and a jet of compressed air removes crystals. The NatSCA and Icon leaflet Care and Conservation of Geological Specimens warns specifically that hard brushing or blasts of compressed air can break fine crystals, and crocoite is the example the warning was written for.
Hollow terminations, and what that means for a description
The Handbook of Mineralogy’s crystal data entry contains a line that quietly settles a lot of arguments between buyer and seller: terminations are commonly hollow or incomplete.
This is a growth feature. A crocoite prism can end in a rectangular opening like a chimney, or simply stop without a proper termination, and neither is breakage. A specimen described as having complete natural terminations and one described as undamaged are therefore different claims, and on crocoite they often come apart.
The distinction is visible under a loupe. A natural hollow termination has faces inside it, with the same lustre and the same orange as the outside. A break has a fresh, duller, more fibrous surface, and on a sectile mineral it often shows a slight smear or step where the crystal sheared. Ask which one you are looking at before you buy, and ask for the photograph that shows it. The questions worth asking are set out on buying minerals online.
Dundas, Beresovsk, and the two British occurrences
The species was described from the Beresovsk district in the Middle Ural Mountains near Yekaterinburg, with type material in the Natural History Museum in Paris, and the name is from the Greek for saffron, an allusion to the colour.
The material that made crocoite famous is Tasmanian. The Dundas district — the Adelaide, West Comet, Heazlewood, Whyte River and Magnet mines — produced it both as exceptional specimens and as an ore of lead, and the archived stock lists of the previous business trading on this domain include a Dundas crocoite with dundasite, which is the classic association.
Britain has two. The Hopeful vein at Leadhills, Lanarkshire, and the Greystone quarry, Lezant, Cornwall. Neither produces anything like Tasmanian material, and both are collector curiosities rather than display pieces — but a labelled British crocoite is a genuinely scarce thing. Our notes on Leadhills and Wanlockhead cover that orefield. Elsewhere: Băița in Romania, Obercallenberg in Saxony, Nontron in the Dordogne, Zimbabwe, the Transvaal, the Philippines, Minas Gerais, and Darwin in California and the Wickenburg mines in Arizona.
Crocoite is an uncommon secondary mineral of oxidised lead deposits associated with chromium-bearing rocks, and the Handbook adds that it may be of post-mine formation. As with langite, that reframes what a locality label is claiming: it fixes where the specimen came from, not necessarily when it grew. See langite for the same problem stated at length.
Handling, storage and the associations to expect
Crocoite is a lead mineral and a chromate. The NatSCA and Icon conservation leaflet puts lead minerals in the group to be handled with gloves and stored in lidded boxes; the same precaution covers the chromium. Wear nitrile gloves, do not generate dust, and wash your hands afterwards. Our page on toxic minerals in a collection sets out which species in a typical drawer need this treatment.
The expected associates are worth knowing because they help confirm a locality: phoenicochroite, vauquelinite, embreyite, pyromorphite, dundasite, vanadinite, descloizite, wulfenite, cerussite, anglesite, quartz and limonite. A crocoite sitting on a gossan with dundasite is telling you it is probably Tasmanian long before the label does.
Crocoite is one of the species we are most often asked to look for, and good undamaged sprays are genuinely hard to find. If you want to be told when we see one, put it on the wanted list. The rest of the species reference covers the lead secondaries it grows with.