Zinnwaldite

Infobox mineral
name = Zinnwaldite
category = Phyllosilicate mineral
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formula = KLiFeAl(AlSi₃)O₁₀(OH,F)₂
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color = Light brown to yellowish- or greenish-white
habit = Micaceous, platey scaly masses, pseudo-hexagonal phenocryst tablets
system = Monoclinic
twinning = On composition plane {001}, twin axis [310] .
cleavage = Perfect basal {001}
fracture = Uneven
mohs = 3.5 - 4.0
luster = Pearly to vitreous
refractive = nα = 1.565 - 1.625 nβ = 1.605 - 1.675 nγ = 1.605 - 1.675
opticalprop = Biaxial (-) 2V = 30°
birefringence = 0.040 - 0.050
pleochroism = distinct
streak = White
gravity = 2.9 - 3.1
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tenacity = Laminae flexible, elastic.
diaphaneity = Transparent to translucent
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Zinnwaldite, KLiFeAl(AlSi₃)O₁₀(OH,F)₂, is a potassium lithium iron aluminium silicate hydroxide fluoride silicate mineral in the mica group.

It occurs in greisens, pegmatite, and quartz veins often associated with tin ore deposits. It is commonly associated with topaz, cassiterite, wolframite, lepidolite, spodumene, beryl, tourmaline, and fluorite.

It was first described in 1845 in Zinnwald/Cinovec on the German-Czech Republic border.

References

* [http://rruff.geo.arizona.edu/doclib/hom/zinnwaldite.pdf Handbook of Mineralogy]
* [http://webmineral.com/data/Zinnwaldite.shtml Webmineral data]
* [http://mindat.org/min-4419.html Mindat]