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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.
Crystal System: Monoclinic
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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