Mineralogy and origin of dumortierite from Girola area, Bhandara district, Eastern Maharashtra

Dumortierite an aluminium borosilicate mineral occurring as aggregates of fibrous, nodular and displaying variable colours is found at Girola hill of Bhandara district. It is associated with kyanite, sillimanite, andalusite, muscovite (sericite), quartz, topaz, rutile, tourmaline and pyrophyllite. It is pink, violet and blue (indigo blue) in colour associated with quartz veins. It shows strong pleochroism from colourless to light pink and pale blue to violet (azure blue). The structural formula of dumortierite is calculated as Si 2.98 Al 6.81 B 0.98 O 18 on the basis of X-ray analysis. Its origin is related to late stage pneumatolytic activity or due to interaction of hydrothermal solution rich in boric acid and titanium dioxide with alumina rich rocks.