Abstract
The chemical compositions of lithium micas in a pegmatite at Minagi, Okayama Prefecture, were studied. This pegmatite consists of five zones; (1) border zone, (2) biotite zone, (3) muscovite zone, (4) zinnwaldite zone and (4) lepidolite zone, arranged inwards successively. Each zone is characterized by their mineral assemblage, especially by the varieties of mica comprised in it.
It appears that iron and magnesium fit better into the mica structure than does lithium, and in the earlier stage the greater part of these elements are removed from the pegmatite solution forming biotite crystals. In the last stage of the cooling history of this pegmatite, the residual solution in which lithium had been gradually concentrated replaced the pre-existing feldspar, producing the lithium micas and secondary greenish violet hydrous alumina minerals. In the later stage, hydrothermal replacement is very remarkable and this is one of the distinctive characteristics of the lithium mica bearing pegmatite.
