| Zinnwaldite | |
| Category: | Phyllosilicate mineral |
| Formula: | KLiFeAl(AlSi3)O10(OH,F)2 |
| Imasymbol: | Znw[1] |
| 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, twin axis [310] |
| Cleavage: | Perfect basal |
| 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 |
| Diaphaneity: | Transparent to translucent |
| References: | [2] [3] |
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.
It was first described in 1845 in Zinnwald/Cinvald (today Cínovec) on the German-Czech Republic border.[4]
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.[5]