Two more new phosphate minerals—tavorite and barbosalite—have been discovered in the Sapucaia pegmatite mine in Minas Gerais, Brazil. Three other minerals recently described were named frondelite, faheyite, and moraesite. The Sapucaia pegmatite is granitic in composition, is zoned on the basis of texture and mineral composition, and has had a significant production of muscovite and beryl.
Tavorite and barbosalite are intimately intergrown secondary phosphate minerals that occur with many other phosphate minerals in the pegmatite, such as heterositc, ferrisicklerite, hureaulite, vivianite, strengite, metastrengite, childrenite, variscite, frondelite, faheyite, moraesite, triphylite, montebrasite, roscherite, and apatite. Other accessory minerals are spodumene, beryl, tourmaline, and sulfides. Quartz, perthite, albite, and muscovite are the essential minerals of the rock.
Tavorite is a hydrous lithium ferric phosphate, the ferric analogue of montebrasite with which it is isostructural. It is named in honor of Dr. Elysairio Tavora, Professor of Mineralogy, Universidade do Brazil, Rio de Janeiro. The mineral occurs as a yellow, very fine grained aggregate with a mean index of refraction of 1.807 and a specific gravity of 3.29. The chemical analysis shows the following percentages: Li2O 7.64, FeO 2.39, MnO 1.47, Fe2O3 42.57, P2O5 39.78, H2O+ 5.76, and H2O-0.40. The formula, as derived from the chemical analysis, is (Li0.90, Fe″0.06, Mn″0.04) Fe‴0.94,(PO4)0.99(OH)1.13 as compared with the ideal formula LiFe (PO4)(OH). X-ray powder data show principal d-spacing (in Å) at 3.045, 3.285, 4.99, 4.68, and 2.474.
Barliosalite is a hydrous ferrous ferric phosphate, the ferric analogue of scorzalite. It is named in honor of A. L. de M. Barbosa, Professor of Geology, Escola de Minas, Minas Gerais, Brazil. The mineral occurs in black nearly opaque grains and masses. Thin grain edges are dark blue green with evident pleochroism. The approximate indices of refraction are: α = 1.77 and γ = 1.835 and the specific gravity is 3.60. The chemical analysis, recalculated to 100 per cent after subtracting admixed tavorite, is: FeO 13.10, MnO 2.82, Fe2O3 41.65, P2O5 37.50, and H2O 4.93 per cent. Its ideal chemical formula is Fe″Fe‴2(PO4)2(OH)2. X-ray powder data indicate principal d-spacings (in Å) at 3.361, 3.313, 4.84, 3.239, 3.160, and 2.327. The mineral is structurally identical with a synthesized compound described by Gheith as ferrous ferric lazulite and both arc closely related to, but have larger cell size than, scorzalite.
Tavorite and barbosalite are examples of complete substitution of trivalent iron for aluminum in known mineral structures.