Riebeckite

minerals

serpentine

magnesio-riebeckite

aegirine

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Formula: ☐Na2(Fe2+3Fe3+2) Si8O22(OH)2 Inosilicate (chain silicate), amphibole
Crocidolite is a fibrous variety of riebeckite or magnesio-riebeckite.
Specific gravity: 3.4
Hardness: 5 to 5½
Streak: Greenish brown
Colour: Black, blue, grey, brown
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Common impurities: Fe,Ti,Mg,Al,Mn
Environments:

Plutonic igneous environments
Pegmatites
Carbonatites
Metamorphic environments

Riebeckite occurs most commonly in igneous rocks such as granite, syenite, nepheline syenite and related pegmatites, and in carbonatites. It is present in some schist of regional metamorphic origin.
Riebeckite also may be found in granite.
In contact metamorphic environments it may be associated with aegirine.

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