Microprobe determinations and X-ray diffraction studies of tapiolite specimens from the granitic pegmatites of the Eräjärvi area, in Orivesi, southern Finland, revealed a new manganesedominant analogue of tapiolite. A small crystal, 1.5 mm long and 0.5 mm thick, from a narrow lithium pegmatite dyke shows some parts richer in Mn than Fe. The name manganotapiolite is used for this Mn-dominant member and ferrotapiolite for the common Fedominant member of the tapiolite group. The tapiolite crystal studied is prismatic, showing poorly developed {100} faces. Manganotapiolite is dark brown, strongly pleochroic from yellowish brown to reddish brown, but thicker fragments are opaque. In reflected light the colour is grey with a weak bireflectance changing from light brownish grey to grey. Internal reflections are strong with red brown colour. The reflectance values measured in

No abstract