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tschermakite
The endmember hornblende tschermakite (☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2) is a calcium rich monoclinic amphibole mineral. It is frequently synthesized along with its ternary solid solution series members tremolite and cummingtonite so that the thermodynamic properties of its assemblage can be applied to solving other solid solution series from a variety of amphibole minerals.
==Mineral composition==
Tschermakite is an end-member of the hornblende subgroup in the calcic-amphibole group. Calcium-rich amphiboles have the general formula X2-3 Y5 Z8 O22 (OH)2 where X=Ca, Na, K, Mn; Y=Mg, Fe+2, Fe+3, Al, Ti, Mn, Cr, Li, Zn; Z=Si, Al (Deer et al., 1963). The structure of tremolite (Ca2Mg5(Si8O22)(OH,F)2), another calcic amphibole, is commonly used as the standard for calcic amphiboles from which the formulae for their substitutions are derived. The wide range in variety of minerals classified in the amphibole group is due to its great ability for ionic replacement resulting in a widely varying chemical composition. Amphiboles can be classified on the basis of the substitution of ions on the X site as well as the substitution of AlAl for Si(Mg, Fe+2). In the calcium amphiboles like tschermakite Ca2(Mg, Fe2+)3Al2 (Si6 Al2) O22(OH)2, the predominant ion in the X position is occupied by Ca as in tremolite, while the substitution MgSi<->AlAl occurs on the Y and the tetrahedral Z site.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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