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Talc carbonates are a suite of rock and mineral compositions found in metamorphic ultramafic rocks. The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions, talc and the carbonate mineral magnesite. Talc carbonate mineral assemblages are controlled by temperature and pressure of metamorphism and the partial pressure of carbon dioxide within metamorphic fluids, as well as by the composition of the host rock.〔(Talc–carbonate alteration of ultramafic rocks within the Leka Ophiolite Complex, Central Norway )〕 ==Compositional controls== In a general sense, talc carbonate metamorphic assemblages are diagnostic of the magnesium content of the ultramafic protolith. * Lower-magnesian ultramafic rocks (12-18% MgO as a rule of thumb) tend to favor talc-chlorite assemblages * Medium-MgO rocks (15-25% MgO) tend to produce talc-amphibole assemblages. * High-MgO rocks with in excess of 25% MgO tend to form true talc-magnesite metamorphic assemblages. Thus, the MgO content of a metamorphosed ultramafic rock can be estimated roughly by understanding the mineral assemblage of the rock. Magnesium content determines the proportion of talc and/or magnesite and aluminium-calcium-sodium content determines the proportion of amphibole and/or chlorite. 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「Talc carbonate」の詳細全文を読む スポンサード リンク
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