The mica group is a group of phyllosilicates (sheet silicates), including muscovite and biotite.
Mica is a common constituent of most pegmatites, granite, diorite, gabbro, andesite and gneiss.
It also may be found in quartzolite, kimberlite, clay, skarn, amphibolite and eclogite.
It is never found in the granulite facies rocks.


The Ma On Shan Mine, Ma On Shan, Sha Tin District, New Territories, Hong Kong, China, is an abandoned iron mine, with both underground and open cast workings. The iron ores contain magnetite as the ore mineral and occur predominantly as masses of all sizes enclosed in a large skarn body formed by contact metasomatism of dolomitic limestone at the margins of a granite intrusion. In parts of the underground workings magnetite is also found in marble in contact with the granite. The skarn rocks consist mainly of tremolite, actinolite, diopside and garnet.
Topaz is found in quartz-mica veins in the granite
Tremolite is found abundantly in the skarn rocks, in intimate association with actinolite; other associated minerals include magnetite, garnet, chlorite, mica and fluorite
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

At Willow Springs, Pinal county, Arizona, USA, mica pseudomorphs after schorl occur in quartz (R&M 94.2.165-166).

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