Zinnwaldite
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- This article is about the mineral. For the color, see Zinnwaldite (color).
| Zinnwaldite | |
|---|---|
| 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. Commonly associated with topaz, cassiterite, wolframite, lepidolite, spodumene, beryl, tourmaline and fluorite.
It was first described in 1845 in Zinnwald (now Cinovec), Czech Republic.
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