The Role of Titanium and the Effect of TiO2 on the Cell-Size, Refractive Index, and Specific Gravity in the Andradite-Melanite- Schorlomite Series

R. A. Howie, A. R. Woolley, J. H. Scoon, R. C. Tyler and J. N. Walsk
Department of Geology, King's College, London, W.C.2
Department of Mineralogy, British Museum (Natural History), Cromwell Road, London, S.W. 7

Summary: New chemical analyses, cell-sizes, and specific gravities are given for 12 garnets, and TiO2 values, cell-sizes, and refractive indices are presented for a further 33 garnets all belonging to the andradite-melanite-schorlomite series. The increase of refractive index, cell-size, and specific gravity with increasing titania is shown graphically. A plot of Ti against Si atoms in the unit cell suggests that Ti replaces Si rather than Fe3+ in the structure, while electron-probe results indicate that Si or (Si+Fe) may be replaced by Ti. The chemical and infra-red absorption data are considered in a discussion of the structural role of titanium in these garnets : both Ti4+ and Ti3+ may be present.

Mineralogical Magazine; June 1968 v. 36; no. 282; p. 775-790; DOI: 10.1180/minmag.1968.036.282.04
© 1968, The Mineralogical Society
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