Crocoite
Crocoite is a mineral consisting of lead chromate, PbCrO4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment.
| Crocoite | |
|---|---|
Crocoite from Dundas, Tasmania | |
| General | |
| Category | Chromate minerals |
| Formula (repeating unit) | Lead Chromate PbCrO4 |
| IMA symbol | Crc |
| Strunz classification | 7.FA.20 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/n |
| Unit cell | a = 7.12 Å, b = 7.421 Å, c = 6.8 Å; β = 102.41°; Z = 4 |
| Identification | |
| Color | Orange, red, yellow; orange-red in transmitted light. |
| Crystal habit | Coarsely crystalline to acicular |
| Cleavage | Distinct on {110} indistinct on {001} and {100} |
| Fracture | Conchoidal to uneven |
| Tenacity | Sectile |
| Mohs scale hardness | 2.5–3 |
| Luster | Adamantine, Sub-Adamantine, Sub-Vitreous, Resinous, Waxy |
| Streak | Yellowish orange |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 5.9–6.1 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 2.290(2) nβ = 2.360(2) nγ = 2.660(2) |
| Birefringence | δ = 0.370 |
| Pleochroism | Weak |
| References | |
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