engleski

Rhodonite group mineral from Morro da Mina mine, Conselheiro Lafaiete, Minas Gerais, Brazil

Deep pink to red, transparent tabular crystals of gem quality were collected at Morro da Mina mine, located in the city of Conselheiro Lafaiete, 115 km south from Belo Horizonte, the capital city of Minas Gerais state, Brazil. The manganese deposits of Morro da Mina are hosted in a metavolcanosedimentary sequence of Archean age, cutted by granodioritic bodies. The regional and contact metamorphism and a sequence of hydrothermal events produced a complex mineralogy, including Mn-bearing minerals rhodonite, pyroxmangite, spessartite and others. According to similar physical properties, the sample was erroneously assumed to be rhodonite. Subsequent X-ray powder diffraction analysis (using CuKα radiation) identified the sample as a mineral belonging to the p-p (pectolite-pyroxene) isostructural series of pyroxenoides, most probably natronambulite. Crystal structure of investigated minerals belonging to p-p isostructural series of pyroxenoides, including nambulite, natronambulite, marsturite and lithiomarsturite, although similar, differs from those of rhodonite, which belongs to the w-p (wollastonite-pyroxene) isostructural series. The differences in their structures are reflected in X-ray diffraction pattern, helping their identification. Further investigation of chemical composition, particularly possible Na, Li, Ca and Mg presence, will help to distinguish mineral member of p-p isostructural series of pyroxenoides. This is the first report of a mineral belonging to this isostructural series from this locality. So far nambulite and natronambulite have been recorded in various localities, including Japan, Namibia and India, all in the metamorphosed manganese ore deposits.

rhodonite group mineral; Morro da Mina mine

nije evidentirano