Formula: KLiFe2+Al(AlSi3O10)(F,OH)2 Monoclinic
Description: Zinnwaldite refers to a dark lithium-rich mica, often an unusual brown, found in some granitic pegmatites. The name is technically discredited, but appears in older literature.
FLORENCE COUNTY: Koehler (1989) reports zinnwaldite as occurring in small euhedral books less than 4.5 mm across in a complex zoned pegmatite in Fern Township (NE NE NW sec. 22 T.39N. R.17E). Associated minerals are amblygonite, spodumene, beryl and quartz.
MARATHON COUNTY: Weidman (1907) described a lithium-rich mica from a quartz-bearing pegmatite in the NW sec. 22 T.29N. R.6E., within the Stettin pluton. He called it a new species, naming it irvingite. Irvingite was later discredited as a species and the mineral described was probably lepidolite. New work suggests the mineral is actually zinnwaldite. (Falster, et. la., 2000). The mineral was found as grayish-white to bright yellow to pale pink micaceous grains up to 2.0 cm. across. The mineral also displayed a parting causing it to break into laths or needles. It is associated with quartz, K feldspar, riebeckite, aegirine, rutile, fluorite, pyrochlore and zircon.