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
Plutonic igneous environments
Riebeckite occurs most commonly in igneous rocks such as granite,
syenite, nepheline syenite
and related pegmatites, and in
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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