Crocoite

From Conservapedia
Jump to: navigation, search
Crocoite
Crocoite1.jpg
Chemical name Lead chromate
Chemical formula PbCrO4
Identification
Birefringence 0.270
Colors Red-orange, cherry red, orange, yellowish
Crystal habit Crystals usually prismatic, striated lengthwise; also acicular, granular, columnar, incrusting, sometimes hollow
Crystal system Monoclinic
Cleavage Distinct, one direction; poor in two other directions. Brittle
Dispersion Strong
Fracture Conchoidal, uneven; brittle and sectile
Hardness 2.5-3
Luster Adamantine to vitreous
Luminescence Weak reddish to dark brown (SW); weaker effect in LW
Name origin From the Greek krokos, meaning saffron, in allusion to the color
Optics α = 2.29-2.31; β = 2.36; λ = 2.66. Biaxial (+), 2V = 57°
Pleochroism Orange-red to blood red
Specific gravity 5.9-6.1
Spectral Distinct band at 5550 but seen only in thin fragments. Transmits mainly in the yellow-red region of the spectrum
Streak Orange-yellow

Occurrence

Secondary mineral in oxidized zones of lead deposits.
Dundas, Tasmania: best crystals found in the world, some gemmy; large clusters.
Beresov Dist., U.S.S.R.: red crystals.
Tiger, Arizona: very tiny crystals.
California
Minas Gerais, Brazil

Comments

Crocoite is one of the loveliest of all collector stones. It's too soft and brittle for wear, but it is quite a rare mineral and relatively few stones have been cut. The dispersion is high but completely masked by the intense body color.

Arem, p. 34
Chesterman, p. 470

Sources

  • Arem, Joel E. Color Encyclopedia of Gemstones, Litton Educational Publishing, Inc.:New York (1977)
  • Chesterman, Charles W. The Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf: New York (1987)