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CategorySilicate mineral
Chemical formulaKFe++Al(Al2Si2)O10(F,OH)2
ColorBlue green, dark brown, black.
Crystal habitMicaceous foliated
Crystal systemMonoclinic - Prismatic 2/m
CleavagePerfect basal
Mohs Scale hardness2.5
LusterVitreous to dull
Refractive indexnα = 1.582 nβ = 1.625 nγ = 1.625
Optical PropertiesBiaxial (-)
Birefringenceδ = 0.043
StreakGreenish gray
Specific gravity3
DiaphaneityTransparent to subopaque

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.


  1. ^ Webmineral
  2. ^ Mindat
  3. ^ Mineral Handbook
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Siderophyllite". A list of authors is available in Wikipedia.
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