Abstract

Alleghanyite, manganhumite and sonolite (the manganese analogues of chondrodite, humite and clinohumite). They are close to end-member Mn minerals in terms of cations but have about 25-30% of hydroxyl replaced by fluorine. Observed partitioning suggests that minor-element substitution does not stabilize one manganese humite relative to another. Qualitative phase equilibria suggest that these assemblages require water-rich conditions to form in silica-undersaturated rocks during regional metamorphism and that variations in XH 2 O/(XH 2 O + XCO 2 ) may account for their formation.--Modified journal abstract.

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