Crystal chemistry of danalite from Daba Shabeli Complex (N Somalia)

Abstract

Danalite is the Fe2+ end-member of the minerals of the helvite group, which have the general formula M8(BeSiO4)6S2, with M = (Mn,Fe2+,Zn). These minerals are relatively uncommon, although limited amounts are known at many localities round the world (e.g. Ragu, 1994; Larsen, 1988; Kwak and Jackson, 1986, and references therein). Their typical host rocks are skams, but occurrences in mineralized veins pegmatites, and altered alkali granites have also been reported. Danalite is rarer than helvite (Mn endmember) and genthelvite (Zn end-member) and, unlike the other two end-members, has never been found nor synthesized as a pure mineral (Mel'nikov et al., 1968).