Zinnwaldite, KLiFeAl(AlSi<sub>3</sub>)O<sub>10</sub>(OH,F)<sub>2</sub>, potassium lithium iron aluminium silicate hydroxide fluoride, is a silicate mineral in the mica group. The IMA status is as a series between siderophyllite (KFe<sub>2</sub>Al(Al<sub>2</sub>Si<sub>2</sub>)O<sub>10</sub>(F,OH)<sub>2</sub>) and polylithionite (KLi<sub>2</sub>AlSi<sub>4</sub>O<sub>10</sub>(F,OH)<sub>2</sub>) and not considered a valid mineral species.
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.