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Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence its name from Latin ''albus''. It is a common constituent in felsic rocks. Albite crystallizes with triclinic pinacoidal forms. Its specific gravity is about 2.62 and it has a Mohs hardness of 6 - 6.5. Albite almost always exhibits crystal twinning often as minute parallel striations on the crystal face. Albite often occurs as fine parallel segregations alternating with pink microcline in perthite as a result of exolution on cooling. There are two variants of albite, which are referred to as ''low albite'' and ''high albite''; the latter is also known as ''analbite''. Although both variants are triclinic, they differ in the volume of their unit cell, which is slightly larger for the ''high'' form. The ''high'' form can be produced from the ''low'' form by heating above c. 750 °C (1382 °F).〔O.F. Tuttle, N.L. Bowen (1950): High-temperature albite and contiguous feldspars. J. Geol. 58(5), 572–583, http://www.jstor.org/stable/30068571〕 Upon further heating to more than c. 1050 °C the crystal symmetry changes from triclinic to monoclinic; this variant is also known as ''monalbite''.〔(Monalbite on Mindat )〕 It occurs in granitic and pegmatite masses, in some hydrothermal vein deposits and forms part of the typical greenschist metamorphic facies for rocks of originally basaltic composition. It was first reported in 1815 for an occurrence in Finnbo, Falun, Dalarna, Sweden.〔 ==References== * (Mineral galleries ) * 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「albite」の詳細全文を読む スポンサード リンク
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