Crocoite
A bright red lead chromate mineral and Tasmanian state emblem.
Crocoite is a mineral consisting of lead chromate, PbCrO4, crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment. S.
- field
- Mineralogy
- known_for
- Bright hyacinth-red prismatic crystals; official Tasmanian mineral emblem
- Mohs_hardness
- 2.5–3
- specific_gravity
- 6.0
- crystal_system
- Monoclinic
- composition
- Lead chromate (PbCrO4)
Lore & Background
Crocoite is commonly found as large, well-developed prismatic adamantine crystals, though many are poorly terminated. The crystals are bright hyacinth-red, translucent, with an adamantine to vitreous lustre; on exposure to UV light some translucency and brilliancy is lost. Its streak is orange-yellow, Mohs hardness 2.5–3, and specific gravity 6.0. At the type locality in the Urals, crystals occur in gold-bearing quartz-veins traversing granite or gneiss, associated with quartz, embreyite, phoenicochroite, and vauquelinite. H. Klaproth.
Reader's Guide
Crocoite is significant both historically and mineralogically. The mineral is identical in composition to chrome yellow, a synthetic paint pigment. Crocoite is the official Tasmanian mineral emblem, and the Adelaide Mine in Dundas, Tasmania, is described as 'probably the prime source of crocoite in the world.' The Adelaide Mining Company Pty. Ltd. The Red Lead Mine, also in Dundas, has produced specimens displayed at the Smithsonian Museum of Natural History. Crocoite's rarity stems from the specific conditions required for its formation: an oxidation zone of lead ore and ultramafic rocks providing chromium. Because it contains lead and hexavalent chromium, crocoite is toxic.
Did You Know?
- Crocoite is identical in composition to the artificial pigment chrome yellow.
- Crocoite is the official Tasmanian mineral emblem.
- The Adelaide Mine in Dundas, Tasmania, is described as 'probably the prime source of crocoite in the world.'
Frequently Asked Questions
What is Crocoite?
Crocoite is a naturally occurring lead chromate mineral (PbCrO4) that forms striking bright hyacinth-red prismatic crystals in the monoclinic system. It is essentially the same compound as the synthetic pigment known as chrome yellow, just found in nature.
How hard is Crocoite and what's its density?
On the Mohs scale, Crocoite sits between 2.5 and 3, making it quite soft and easy to scratch. Despite its delicate appearance, it is surprisingly dense at a specific gravity of 6.0, owing to the lead in its structure.
What is Crocoite's connection to Tasmania?
Crocoite holds the distinction of being the official mineral emblem of Tasmania, Australia. It is a locally significant find that has become a point of pride for the island state's geological heritage.
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