Riebeckite is a member of the amphibole group. It has the chemical formula of Na2(Fe,Mg)3Fe2Si8O22(OH)2. Riebeckite is a common mineral, but is usually not reco — Photo: Shannon Heinle · CC0
Riebeckite
Also known as: Crocidolite (fibrous var.).
A sodium-iron amphibole — the blue 'crocidolite' asbestos fibers are its fibrous variety.
Intro adapted from Wikipedia (CC BY-SA).
Riebeckite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₂(Fe²⁺₃Fe³⁺₂)Si₈O₂₂(OH)₂.
It crystallizes in the monoclinic crystal system. It is a member of the Amphibole structural group.
Key properties: Mohs hardness 5–6; specific gravity 3.28–3.44; typically blue or black; bluish-gray streak; Vitreous to silky luster; optically biaxial.
IMA symbol Rbk, IMA status: approved, named in 1888.
Found in alkalic granites and syenites; rarer in felsic volcanics and granite pegmatites; in some schists. In iron formations as asbestiform \crocidolite.".
It is found associated with Aegirine, nepheline, albite, arfvedsonite (igneous); tremolite, ferro-actinolite (metamorphic); grunerite, magnetite, hematite, stilpnomelane, ankerite.
The mineral was named to honor Emil Riebeck (1853–1885), German explorer. All rights reserved. No par t of t his publication may b e reproduced.
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