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The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms. The word ''mica'' is derived from the Latin word ''ラテン語:mica'', meaning ''a crumb'', and probably influenced by ''ラテン語:micare'', to glitter. ==Classification== Chemically, micas can be given the general formula〔Deer, W. A., R. A. Howie and J. Zussman (1966) ''An Introduction to the Rock Forming Minerals'', Longman, ISBN 0-582-44210-9〕 :''X''2''Y''4–6''Z''8O20(OH,F)4 in which : ''X'' is K, Na, or Ca or less commonly Ba, Rb, or Cs; :''Y'' is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.; :''Z'' is chiefly Si or Al, but also may include Fe3+ or Ti. Structurally, micas can be classed as dioctahedral (''Y'' = 4) and trioctahedral (''Y'' = 6). If the ''X'' ion is K or Na, the mica is a ''common'' mica, whereas if the ''X'' ion is Ca, the mica is classed as a ''brittle'' mica. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mica」の詳細全文を読む スポンサード リンク
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