HINGGANITE-(Y) FROM THE ZOMBA-MALOSA COMPLEX, MALAWI

The rare mineral hingganite-(Y) has been identified in agpaitic granit e pegmatites in alkaline granites from the northern-Malosa-part of the Zomba-Malosa complex of the Chilwa alkaline province, Malawi. The par agenesis closely resembles the paragenesis of the pegmatite at Narssar ssuk, South Greenland and contains potassium feldspar, albite, aegirin e, arfvedsonite, riebeckite var. crocidolite, quanz, zircon, pyrochlor e, epididymite, eudidymite, polylithionite, mangan-neptunite, parisite -(Ce), bastnasite-(Ce), fergusonite-(Y), hematite, goethite, ilmenite, rutile (?) and hingganite-(Y). The hingganite-(Y) forms 1 mm individu al crystals and fan- and sheaf-shaped aggregates, up to almost 2 mm. T he crystals are pale bluish and transparent with a vitreous lustre. Th e larger crystals are dominated by {110} and {111} with only minor fac es of {001}; simpler crystals show only {110} and {001}. Optically the Malawi hingganite-(Y) is biaxial positive with 2V(alpha) meas. = 117/-3-degrees, n(alpha) = 1.7446+/-0.0005, n(beta) = 1.7518+/-0.0005 and n(gamma) = 1.7729+/-0.0005, 2V(alpha) calc. = 119+/-3-degrees; beta = b, gamma OR c = 13-degrees in the acute angle beta. The unit cell par ameters of the hingganite-(Y) from Malawi are: a = 4.733+/-0.003, b = 7.606+/-0.003, c = 9.895+/-0.006 angstrom and beta = 90.347+/-0.001-de grees. Both the optical properties and the unit cell parameters corres pond well with those presented for hingganite-(Y) from the type locali ty - Greater Khingan area, China. The chemical composition of the Mala wi hingganite-(Y) has been established by electron microprobe and by o ptical emission spectrographic analyses for Be. The chemical compositi on of the hingganite-(Y) from Malawi corresponds well with that presen ted for hingganite-(Y) from Japan; compared to hingganite - (Y) from t he type locality the Malawi hingganite-(Y) is very much enriched in Y.