| Zinnwaldite | |
|---|---|
 Fluorapatite with topaz on zinnwaldite and quartz | |
| General | |
| Category | Phyllosilicate mineral |
| Formula (repeating unit) | KLiFeAl(AlSi3)O10(OH,F)2 |
| IMA symbol | Znw |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | Cc (no. 9) |
| Unit cell | a = 5.29, b = 9.14 c = 10.09 ; β = 100.83° |
| Identification | |
| Color | Gray-brown, yellow-brown, pale violet, dark green, color zoning common |
| Crystal 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 |
| Cleavage | Perfect basal {001} |
| Fracture | Uneven |
| Tenacity | Laminae °exible, elastic |
| Mohs scale hardness | 3.5 - 4.0 |
| Luster | Pearly to vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.9 - 3.1 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.565 - 1.625 nβ = 1.605 - 1.675 nγ = 1.605 - 1.675 |
| Birefringence | 0.040 - 0.050 |
| Pleochroism | Distinct, X = colorless to yellow-brown; Y = gray-brown; Z = colorless to gray-brown |
| 2V angle | 0 - 40° |
| 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.
Occurrence
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.
References
- Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Handbook of Mineralogy
- Webmineral data
- ^ Mindat
- Rieder, M.; Hybler, J.; Smrcok, L.; Weiss, Z. (1996). "Refinement of the crystal structure of zinnwaldite 2M_1". European Journal of Mineralogy. 8 (6): 1241–1248. doi:10.1127/ejm/8/6/1241.
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