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Riebeckite facts for kids

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Crystals of black riebeckite in alkaline pegmatite, near Évisa (Corsica, France).jpg
Black riebeckite in an alkaline pegmatite from Lindinosa near Évisa, Corsica, France
Category Silicate mineral
(repeating unit)
Crystal symmetry Monoclinic 2/m
Unit cell a = 9.76 Å, b = 18.04 Å, c = 5.33 Å; β = 103.59°; Z=2
Color Black, dark blue; dark blue to yellow-green in thin section
Crystal habit As prismatic crystals, commonly fibrous, asbestiform; earthy, massive
Crystal system Monoclinic - Prismatic
Twinning Simple or multiple twinning parallel to {100}
Cleavage Perfect on {110}, intersecting at 56° and 124°; partings on {100} and {010}
Fracture Conchoidal to uneven
Tenacity Brittle
Mohs scale hardness 6
Luster Vitreous to silky
Streak Pale to bluish gray
Diaphaneity Semitransparent
Specific gravity 3.28–3.44
Optical properties Biaxial (-)
Refractive index nα = 1.680–1.698 nβ = 1.683–1.700 nγ = 1.685–1.706
Birefringence δ = 0.005–0.008
Pleochroism X = blue, indigo; Y = yellowish green, yellow brown; Z = dark blue
2V angle Measured: 68° to 85°, Calculated: 62° to 78°
Dispersion Strong

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.

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