Sinhalite and serendibite from Tanzania

EVER since Claringbull and Hey 0952) first described the mineral sinhalite, which had previously been identified as gem peridot, other discoveries have been reported (Meixner, I953; Zwaan, I955; Payne, ~958; Giibelin, 1962). Essentially sinhalite is found in skarn assemblages from contact zones of metamorphosed carbonate rocks with, for example, Archean gneiss (Aldan massif, U.S.S.R., Shabynin, I956) or granite (Warren County, New York, U.S.A., Schaller and Hildebrand, 1955)It is mineralogically similar to forsteritic olivine but can be distinguished by its higher refractive indices, specific gravity, and a much smaller optic axial angle. Chemically, boron substitutes for silicon and part of the magnesium is replaced by aluminium in the olivine structure. Optical absorption spectra have also shown that minor but significant amounts of iron are present as Fe 2+ giving a chemical composition of AlMg0.95Feo.05BO4 (Fang and Newnham, 1965). This paper discusses a further occurrence of sinhalite in a skarn assemblage from the Handeni district, north-east Tanzania. The mineral was provisionally identified by the writers during I964 in a sample of calcitic marble from the Kwakonje area. A brief note on this occurrence has already been published by one of us (yon Knorring, I967); additional information on the locality and the associated minerals including serendibite and warwickite is given in this communication. It is worth noting that this is the first recorded in situ locality of sinhalite in the African continent. The locality in Tanzania is known for its production of gem quality tourmaline, blue and red spinels, and the occasional ruby. More recently kornerupine was identified by Dr. R. A. Howie (personal communication) in a marble collected from the