Amphiboles from the Younger Granites of Nigeria. Part II. X-Ray Data

M. T. Frost
Department of Geology, The University, Manchester.1
1Present address: Department of Mineralogy, British Museum (Natural History), Cromwell Road, London, S.W. 7.

Summary: The cell parameters of fifteen arfvedsonites and four ferrohastingsites were determined using powder and diffractometer techniques and a least squares method of computation. Methods are proposed of distinguishing between calcium- and sodium-rich amphiboles, and between iron-rich and iron-poor varieties of these two groups, by their powder data. Within the arfvedsonite group the b parameter was found to increase with increasing Ca, Fe″, and (OH) and to decrease with increasing Na, F, and Li. The c parameter was found to decrease with increasing F and increase with increasing (Fe‴+Al+Ti). The parameters a, β, and a sin β alltended to increase withincreasing Ca, Fe″, and F content. The cell volumes were found to vary with the b parameter. The ferrohastingsites were found to have much larger cell parameters than the arfvedsonites. An attempt was made to explain these variations from structural considerations.

Mineralogical Magazine; March 1963 v. 33; no. 260; p. 377-384; DOI: 10.1180/minmag.1963.033.260.03
© 1963, The Mineralogical Society
Mineralogical Society (