The phyllites (q.v.) form a middle term between this group and the slates; they consist usually of quartz, white mica and chlorite, and have much of the foliation and schistosity of the mica-schists.
The spots contain variety of minerals, sometimes mainly white mica or chlorite.
These crystals may be half an inch to several inches in length; they are usually more or less completely weathered to white mica and kaolin.
The felspar decomposes into kaolin and quartz; its alkalis are for the most part set free and removed in solution, but are partly retained in the white mica which is constantly found in crude china-clays.
As before stated tin will never be found far from granite, and that granite must have white mica as one of its constituents.
Angular quartz and a variable quantity of white mica up to 0. 1mm across.
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