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Formula: KFe2+2Al(Si2Al2)O10(OH)2
Phyllosilicate (sheet silicate), biotite subgroup, forms a series
with
polylithionite
Crystal System: Monoclinic
Specific gravity: 3.1 measured, 3.17 calculated
Hardness: 2½
Streak: Greenish grey
Colour: Dark green, brown, black
Solubility:
Common impurities: Ti,Mn,Mg,Ca,Li,Na,Rb,Cs,Cl,H2O
Environments:
Plutonic igneous environments
Pegmatites
Siderophyllite occurs in pegmatites in nepheline syenite, in
greisen, in granite and in
aplite
(HOM).
Localities
At the type locality, Pikes Peak, El Paso county, Colorado, USA, siderophyllite is associated with
microcline and astrophyllite
(HOM).
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