SIMPSONITE AND THE NORTHERN BRAZILIAN PEGMATITE REGION
A study of the Alto do Giz, near Equador, Rio Grande do Norte, Brazil, reveals an interesting series of tantalum minerals including the rare aluminum tantalate, simpsonite. Crystals of this mineral are yellow brown, hexagonal in outline; c = .60978. It belongs to the hexagonal dipyramidal class C 6h . Hardness 7½, specific gravity is 6.81. It fluoresces blue to white in a cold quartz mercury vapor lamp with a filter. It is also found in white crystals at this mine and in buff-colored crystals at the Onca Mine, some miles away. It appears to be a replacement mineral of a short complex pegmatite sequence, crystallizing after microlite and tantalite.