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Black riebeckite in an alkaline pegmatite from Lindinosa near Évisa, Corsica, France
CategorySilicate mineral
(repeating unit)
Crystal symmetryMonoclinic 2/m
Unit cella = 9.76 Å, b = 18.04 Å, c = 5.33 Å; β = 103.59°; Z=2
ColorBlack, dark blue; dark blue to yellow-green in thin section
Crystal habitAs prismatic crystals, commonly fibrous, asbestiform; earthy, massive
Crystal systemMonoclinic - Prismatic
TwinningSimple or multiple twinning parallel to {100}
CleavagePerfect on {110}, intersecting at 56° and 124°; partings on {100} and {010}
FractureConchoidal to uneven
Mohs scale hardness6
LusterVitreous to silky
StreakPale to bluish gray
Specific gravity3.28–3.44
Optical propertiesBiaxial (-)
Refractive indexnα = 1.680–1.698 nβ = 1.683–1.700 nγ = 1.685–1.706
Birefringenceδ = 0.005–0.008
PleochroismX = blue, indigo; Y = yellowish green, yellow brown; Z = dark blue
2V angleMeasured: 68° to 85°, Calculated: 62° to 78°

Riebeckite is a silicate mineral. It is found in nature as both a fibrous form and a solid form. The fibrous form, called blue asbestos or crocidolite asbestos, is one of the six types of asbestos. It is considered by many experts to be the most dangerous type of asbestos. It can cause cancer and asbestosis. It was formerly used in Kent brand cigarettes as a filter material. It is rare in construction compared to white asbestos, but it is sometimes found in caulking, cement, wallboard, rope, and numerous other products. Due to its hazards, blue asbestos is no longer mined commercially.

Related pages[change | change source]

Sources[change | change source]

  1. "Riebeckite", Handbook of Mineralogy, Mineral Data Publishing, 2001
  2. "Riebeckite", Mindat.org
  3. "Riebeckite", The Mineralogy Database (webmineral.com)
  4. IMA Master List

Other websites[change | change source]

  • Chisholm, Hugh, ed. (1911). "Crocidolite" . Encyclopædia Britannica. Vol. 7 (11th ed.). Cambridge University Press. p. 477.