'Greisen' definitions:

Definition of 'greisen'

(from WordNet)
noun
A granitic rock composed of quartz and mica

Definition of 'Greisen'

From: GCIDE
  • Greisen \Grei"sen\, n. (Min.) A crystalline rock consisting of quarts and mica, common in the tin regions of Cornwall and Saxony. [1913 Webster]