Crocoite
Crocoite is lead chromate, PbCrO4, prized for its vivid orange-red color and slender, elongated prismatic crystals that rank among the most vibrantly colored of any mineral. It forms in the oxidized zones of lead deposits where chromium-bearing solutions interact with lead minerals, a fairly uncommon geochemical pairing. It holds historical significance as the first mineral source of the element chromium, discovered and named in the late 18th century.
Crocoite properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | PbCrO4 |
| Mohs hardness | 2.5–3 |
| Crystal system | Monoclinic |
| Luster | Adamantine to vitreous/resinous |
| Streak | Orange-yellow |
| Cleavage | Distinct on {110} |
| Fracture | Conchoidal to uneven, brittle to sectile |
| Specific gravity | 5.9–6.1 |
| Transparency | Translucent |
| Common colors | Bright orange-red, Red |
| Rarity | common |
Geology & background
Crocoite forms through the oxidation and weathering of lead ores in the presence of chromium, typically sourced from nearby chromite-bearing ultramafic rocks, a combination of chemistries met in only a handful of places worldwide. The single most important locality by far is the Dundas mining district of Tasmania, Australia, where slender, gemmy orange-red crystals reaching several inches long have been recovered from cavities in weathered lead-zinc veins. Smaller occurrences are known from Russia's Ural Mountains, where the mineral was first described in 1766, along with Congo and parts of the United States.
Crocoite specimens from Tasmania rank among the most sought-after mineral aesthetics in the world, commanding high prices for well-formed crystal sprays with strong color saturation and minimal damage. Because crystals are thin, brittle, and easily broken, careful handling and stable storage away from vibration are essential for preserving specimen value. Collectors should also know that crocoite is somewhat light-sensitive and can lose luster if displayed under strong, prolonged illumination.
How to identify Crocoite
Crocoite displays a bright orange to red color with an adamantine to vitreous luster and a distinctive orange-yellow streak, immediately setting it apart from most other minerals. It is soft and brittle, with a hardness around 2.5 to 3 and imperfect cleavage, forming slender prismatic to acicular crystals often in radiating or parallel groups. Its vivid, saturated color combined with an elongated crystal habit makes misidentification unlikely, though it can superficially resemble wulfenite or vanadinite by color alone.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Crocoite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Crocoite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Crocoite was the original source from which the element chromium was first isolated in 1797, and it also gave chromium its name, from the Greek word for color.
- The Dundas district of Tasmania has produced crocoite crystals considered among the finest mineral specimens in the world.
- Crocoite's slender crystals are so fragile that specimen collectors often display them under glass domes to guard against accidental damage from air currents.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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