Siderophyllite

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Siderophyllite
Category Silicate mineral
Chemical formula KFe++Al(Al2Si2)O10(F,OH)2
Identification
Color Blue green, dark brown, black.
Crystal habit Micaceous foliated
Crystal system Monoclinic - Prismatic 2/m
Cleavage Perfect basal
Fracture Conchoidal
Mohs Scale hardness 2.5
Luster Vitreous to dull
Refractive index nα = 1.582 nβ = 1.625 nγ = 1.625
Optical Properties Biaxial (-)
Birefringence δ = 0.043
Streak Greenish gray
Specific gravity 3
Diaphaneity Transparent to subopaque
References [1][2][3]

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.

[edit] References

  1. ^ http://webmineral.com/data/Siderophyllite.shtml Webmineral
  2. ^ http://www.mindat.org/min-3651.html Mindat
  3. ^ http://rruff.geo.arizona.edu/doclib/hom/siderophyllite.pdf Mineral Handbook
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