Riebeckite forms in two very different habits. The darker-colored forms which are individually crystallized are generally of igneous origin, such as volcanic rock and pegmatites. The finely fibrous variety, known as Crocidolite, usually originates from altered metamorphic rocks. The Crocidolite variety is a type of asbestos, and is sometimes also referred to as “blue asbestos”.
It is considered to be the most hazardous form of asbestos, and should never be brought near the mouth. If its fibers or particles enter the lungs, they can cause asbestosis. Asbestosis is a lung disease caused by inhalation of asbestos particles, which causes several cancers, particularly lung cancer and mesothelioma. Symptoms of asbestosis do not arise until about 20 years after the inhalation. Due to the hazards, washing hands after handling specimens is highly recommended. Many mineral collectors avoid collecting asbestos minerals out of safety concerns.
Chemical Formula: [Na2][Z32+Fe23+]Si8O22(OH,F,Cl)2
Locality: Socotra island, Indian Ocean, Yemen.
Name Origin: Named after the German traveler, Emil Riebeck (1853-1885).
Physical Properties
Cleavage: {110} Perfect, {???} Perfect
Color: Blue, Black, Dark green.
Density: 3.4
Diaphaneity: Translucent to subtranslucent to opaque
Fracture: Brittle – Uneven – Very brittle fracture producing uneven fragments.
Hardness: 4 – Fluorite
Luminescence: Non-fluorescent.
Luster: Vitreous – Silky
Magnetism: Nonmagnetic
Streak: greenish brown
Color: Blue, Black, Dark green.
Density: 3.4
Diaphaneity: Translucent to subtranslucent to opaque
Fracture: Brittle – Uneven – Very brittle fracture producing uneven fragments.
Hardness: 4 – Fluorite
Luminescence: Non-fluorescent.
Luster: Vitreous – Silky
Magnetism: Nonmagnetic
Streak: greenish brown
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