Zinnwaldite
General
Category	Phyllosilicate mineral
Chemical formula	KLiFeAl(AlSi3)O10(OH,F)2
Identification
Color	Light brown to yellowish- or greenish-white
Crystal habit	Micaceous, platey scaly masses, pseudo-hexagonal phenocryst tablets
Crystal system	Monoclinic
Twinning	On composition plane {001}, twin axis [310].
Cleavage	Perfect basal {001}
Fracture	Uneven
Tenacity	Laminae flexible, elastic.
Mohs Scale hardness	3.5 - 4.0
Luster	Pearly to vitreous
Refractive index	nα = 1.565 - 1.625 nβ = 1.605 - 1.675 nγ = 1.605 - 1.675
Optical Properties	Biaxial (-) 2V = 30°
Birefringence	0.040 - 0.050
Pleochroism	distinct
Streak	White
Specific gravity	2.9 - 3.1
Diaphaneity	Transparent to translucent

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

• Handbook of Mineralogy
• Webmineral data
• Mindat

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