ZINNWALDITE

Zinnwaldite is a name that was given to a dark lithium-bearing mica that occurs in a cassiterite-mineralized greisen in the locality of Cínovec (formerly “Zinnwald” = “tin forest”) in the Czech Republic, near the border with Germany.

The name was discredited in 1998 and therefore zinnwaldite is no longer considered a mineral species, but only a mica of the siderophyllite-polylithionite series. In several sources (books, etc.) zinnwaldite is still listed as a mineral species. Therefore, care must be taken with the bibliography.

It occurs in greisen (pneumatolytic deposits with Sn), rarely in granites, granitic pegmatites and high-temperature quartz veins.

This mica is associated with quartz (rock crystal, smoky), plagioclase (albite), potassium feldspars (orthoclase, microcline), garnet (spessartine), cassiterite, wolframite, lepidolite, spodumene, beryl, tourmaline, scheelite, fluorite, and topaz (pyknite).

Zinnwaldite 01: In PPL, in the center of the image, "zinnwaldite" with its first pleochroism color. Surrounding it are quartz (colorless and low relief) and topaz (colorless and high relief). The rock is that with cassiterite from the historic locality of "Zinnwald".
Zinnwaldite 01: Again in PPL, the same section of the previous image, now rotated 90 degrees and showing the second color of pleochroism of zinnwaldite. It is a clear pleochroism, easy to perceive, but much clearer than the pleochroism of biotites.
Zinnwaldite 01: The same crystal of the former two images, now in XPL. It looks very much like muscovite.
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