Crocoite

Crocoite
Crocoite from Dundas, Tasmania
General
CategoryChromate minerals
Formula
(repeating unit)
Lead Chromate PbCrO4
IMA symbolCrc[1]
Strunz classification7.FA.20
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/n
Unit cella = 7.12 Å, b = 7.421 Å,
c = 6.8 Å; β = 102.41°; Z = 4
Identification
ColorOrange, red, yellow; orange-red in transmitted light.
Crystal habitCoarsely crystalline to acicular
CleavageDistinct on {110} indistinct on {001} and {100}
FractureConchoidal to uneven
TenacitySectile
Mohs scale hardness2.5–3
LusterAdamantine, Sub-Adamantine, Sub-Vitreous, Resinous, Waxy
StreakYellowish orange
DiaphaneityTransparent to translucent
Specific gravity5.9–6.1
Optical propertiesBiaxial (+)
Refractive indexnα = 2.290(2) nβ = 2.360(2) nγ = 2.660(2)
Birefringenceδ = 0.370
PleochroismWeak
References[2][3][4]

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.[5]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ "Crocoite (PbCrO4)" (PDF). Rruff.geo.arizona.edu. Retrieved 19 December 2016.
  3. ^ "Crocoite: Crocoite mineral information and data". Mindat.org. 15 December 2016. Retrieved 19 December 2016.
  4. ^ "Crocoite Mineral Data". Webmineral.com. Retrieved 19 December 2016.
  5. ^ Chisholm 1911.