Ca-Fe2+-rich, graftonite-related phosphate from fossil pyrometamorphic rocks from Nechvalice, Most Basin, Czech Republic
Abstract
Ca-Fe-rich to Ca-dominant anhydrous phosphate close to graftonite (27.73-30.58 wt. % FeOtot, 21.06-22.71 wt. % CaO) occurs as a late primary accessory phase of combustion metamorphic buchite of Pleistocene age in Nechvalice in the Neogene Most Basin in Czech Republic. It occurs as brown translucent anhedral grains up to 200 /jm long filling the interstices between dominant euhedral fayalite crystals associated with minor anorthite, hercynite-magnetite, glass and amorphous hydrated Fe-phosphosilicate. The empirical formula of Ca-rich graftonite-related phosphate ranges between: (Fe -i.21-1 .39Ca1.19-1.31Mg0.33-0.46Mn0.03-0.05)X2,95-3.10P1.94-2.0008- At least the Ca-richest chemical compositions can be classed as a distinct species, an unnamed Ca-dominant analogue of graftonite, (Ca, Fe2+, Mg, Mn)3(P04)2