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Forsterite (Mg2SiO4; commonly abbreviated as Fo) is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite. Forsterite crystallizes in the orthorhombic system (space group ''Pbnm'') with cell parameters ''a'' 4.75 Å (0.475 nm), ''b'' 10.20 Å (1.020 nm) and ''c'' 5.98 Å (0.598 nm).〔 Forsterite is associated with igneous and metamorphic rocks and has also been found in meteorites. In 2005 it was also found in cometary dust returned by the Stardust probe. In 2011 it was observed as tiny crystals in the dusty clouds of gas around a forming star.〔(Spitzer sees crystal 'rain' in outer clouds of infant star ), Whitney Clavin and Trent Perrotto, Physorg.com, May 27, 2011 . Accessed May 2011〕 Two polymorphs of forsterite are known: wadsleyite (also orthorhombic) and ringwoodite (isometric). Both are mainly known from meteorites. Peridot is the gemstone variety of forsterite olivine. Forsterite reacts with quartz to form the orthopyroxene mineral enstatite in the following reaction: :Mg2SiO4 + SiO2 → 2MgSiO3. ==Composition== Pure forsterite is composed of magnesium, oxygen and silicon. The chemical formula is Mg2SiO4. Forsterite, fayalite (Fe2SiO4) and tephroite (Mn2SiO4) are the end-members of the olivine solid solution series; other elements such as Ni and Ca substitute for Fe and Mg in olivine, but only in minor proportions in natural occurrences. Other minerals such as monticellite (CaMgSiO4), an uncommon calcium-rich mineral, share the olivine structure, but solid solution between olivine and these other minerals is limited. Monticellite is found in contact metamorphosed dolomites.〔 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「forsterite」の詳細全文を読む スポンサード リンク
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