Siderophyllite

Infobox mineral
name = Siderophyllite
category = Silicate mineral
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formula = KFe⁺⁺Al(Al₂Si₂)O₁₀(F,OH)₂
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color = Blue green, dark brown, black.
habit = Micaceous foliated
system = Monoclinic - Prismatic 2/m
twinning =
cleavage = Perfect basal
fracture = Conchoidal
mohs = 2.5
luster = Vitreous to dull
refractive = nα = 1.582 nβ = 1.625 nγ = 1.625
opticalprop = Biaxial (-)
birefringence = δ = 0.043
pleochroism =
streak = Greenish gray
gravity = 3
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diaphaneity = Transparent to subopaque
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references = [http://webmineral.com/data/Siderophyllite.shtml Webmineral] [http://www.mindat.org/min-3651.html Mindat] [http://rruff.geo.arizona.edu/doclib/hom/siderophyllite.pdf Mineral Handbook]

Siderophyllite is a rare member of the mica group of silicate minerals with formula: KFe⁺⁺Al(Al₂Si₂)O₁₀(F,OH)₂

The mineral occurs in nepheline syenite pegmatites and granite and aplite greisens. It is associated with microcline and astrophyllite at Pikes Peak, Colorado. It is also found in the alkali pegmatites of Mont Saint-Hilaire, Quebec.

It was first described in 1880 for an occurrence near Pikes Peak, Colorado. The name derives from the Greek "sideros", iron, plus "phyllon", leaf, in reference to its iron rich composition and perfect basal cleavage.

References