Granite Railway Quarry (Granite Rail Quarry), Quincy, Norfolk Co., Massachusetts, USA © 2004 Peter Cristofono
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

Photos :

This sample of the crocidolite variety of riebeckite is from Todos Santos, Cochabamba, Bolivia. The center bundle is about 25 cm high. These samples of crocidolite are displayed in the Smithsonian Museum of Natural History.
The sample is about 15 cm across and is from Carn Brea mine, Prieska district, Cape Province, South Africa. These samples of crocidolite are displayed in the Smithsonian Museum of Natural History.
Riebeckite Root Name (Var: Crocidolite), Pyrite Locality: Griqualand, Northern Cape Province, South Africa Dimensions: 5.2 cm x 3.2 cm x 2.9 cm Copyright © Jasun McAvoy & mineralman
Riebeckite Root Name (Var: Crocidolite), Hematite, Quartz, Tiger’s Eye Locality: Brockman Tiger eye mine (Marra Mamba), Mount Brockman, Ashburton Shire, Western Australia, Australia Dimensions: 185 mm x 80 mm Field of View: 180 mm Copyright © Andrew Tuma