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Crocoite Mineral Facts:

Chemical Formula: PbCrO₄ 68.9% Lead Oxide

Colors: Bright Red. Streak is orange-yellow.

Hardness: 2.5 to 3.0

Density: 5.9 to 6.1 

Cleavage: One distinct cleavage.

Crystallography: Monoclinic

Luster:. Adamantine luster. Usually translucent.

Optics: (Refractive Index):  2.42

Composition, Structure and Associated Minerals:
Crocoite is a rare mineral found in the oxidized zones of lead veins. It is the only chromate of importance, among minerals, is the lead salt of normal chromic acid, H2CrO4. There are several other chromates known, but they are basic salts and are rare. All are lead compounds. The normal salt, PbCrO4, is known as crocoite. Chromic acid is unknown, as it spontaneously breaks down into CrO3 and water when set free from its salts.

Crocoite is well characterized by its hyacinth-red color. It occurs with lead minerals and in some quartz veins, and is formed by secondary reactions with the weathering forces of water and air. It is frequently associated with pyromorphite, cerussite and wulfenite.

Identification and Diagnostics
The mineral is easily recognized by its color and the test for chromium. If heated on charcoal it is reduced to metallic lead with deflagration, and coats the charcoal with an encrustation of chromium and lead oxides. Tested with a borax bead, it yields an emerald green color.

Occurrence, Localities and Origins:
A rare secondary lead mineral, it is found in very few lead deposits. World wide, it is found at Beresof in the Urals; at Rezbanya and Moldawa, in Romania; the Philippine Islands, and in Tasmania. Fine crystal specimens (as shown in the photographs) come from Mount Dundas, Tasmania. In the US it has been found in the Vulture Mining district, Maricopa Co., Arizona.

Its occurrence is too rare to be valuable as an ore of lead or chrome, but it is of historical note since the element chromium was first discovered by virtue of its presence in crocoite.

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