What is "greisen"

Greisen \Grei"sen\, n. (Min.) A crystalline rock consisting of quarts and mica, common in the tin regions of Cornwall and Saxony.

n. (context geology English) A highly altered granitic rock containing quartz and mica

n. a granitic rock composed of quartz and mica

Greisen is a highly altered granitic rock or pegmatite. Greisen is formed by self-generated alteration of a granite and is a class of endoskarn.

Greisens appear as highly altered rocks, partly coarse, crystalline granite, partly vuggy with miarolitic cavities, disseminated halide minerals such as fluorite, and occasionally metallic oxide and sulfide ore minerals, borate minerals ( tourmaline) and accessory phases such as sphene, beryl, topaz, etcetera.