zinnwaldite

{{Infobox mineral | name = Zinnwaldite | category = Phyllosilicate minerals | group = Mica group, trioctahedral mica group | boxwidth = | boxbgcolor = | image = Fluorapatite-Quartz-Topaz-gha5a.jpg | caption = Fluorapatite with topaz on zinnwaldite and quartz | formula = KLiFeAl(AlSi3)O10(OH,F)2 | IMAsymbol = Znw | molweight = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = Cc (no. 9) | unit cell = a = 5.29, b = 9.14 c = 10.09 [Å]; β = 100.83° | color = Gray-brown, yellow-brown, pale violet, dark green, color zoning common | habit = Well-formed short prismatic or tabular crystals, pseudohexagonal, in rosettes or fan-shaped groups; lamellar or scaly aggregates; disseminated. | twinning = On composition plane {001}, twin axis [310] | cleavage = Perfect basal {001} | fracture = Uneven | tenacity = Laminae °exible, elastic | 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 (-) | birefringence = 0.040 - 0.050 | pleochroism = Distinct, X = colorless to yellow-brown; Y = gray-brown; Z = colorless to gray-brown | 2V = 0 - 40° | streak = White | gravity = 2.9 - 3.1 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | references = }} Zinnwaldite, KLiFeAl(AlSi3)O10(OH,F)2, potassium lithium iron aluminium silicate hydroxide fluoride, is a silicate mineral in the mica group. The IMA status is as a series between siderophyllite (KFe2Al(Al2Si2)O10(F,OH)2) and polylithionite (KLi2AlSi4O10(F,OH)2) and not considered a valid mineral species.

==Name and discovery== It was first described in 1845 in Zinnwald/Cinvald (today Cínovec) on the German-Czech Republic border.