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Grovesite, the manganese-rich analogue of berthierine

Published online by Cambridge University Press:  14 March 2018

F. A. Bannister ,
M. H. Hey  and
W. Campbell Smith
F. A. Bannister
Affiliation:
Department of Mineralogy, British Museum (Natural History)
M. H. Hey
Affiliation:
Department of Mineralogy, British Museum (Natural History)
W. Campbell Smith
Affiliation:
Department of Mineralogy, British Museum (Natural History)
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Abstract

A Dark brown (blackish-brown) mineral forms a thin crust on manganese ore on the specimen [B.M. 1944,35] from no. 5 orebody of the Benallt mine, Rhiw, Carnarvonshire, North Wales. This is the specimen on which the first measurable crystals of banalsite were discovered in 1944 (Min. Mag., 1945, vol. 27, pp. 63-64). The mineral occurs as closely-packed, small rosettes, at most 0"5 ram. across, and is partly coated with a thin layer of baryte. An X-ray photograph by Dr. Bannister suggested that the mineral might belong to the chlorite group. Its optical properties were determined and nothing further was done with it at the time.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 30 , Issue 229 , June 1955 , pp. 645 - 647
Copyright
Copyright © 1955, The Mineralogical Society

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References

Note

1 Chamosite (Berthier, 1820, originally from Chamoson, Switzerlands and berthierine (Beudant, 1832, originally from I-Iayanges, France) have long been supposed to be identical, but a variety of evidence recently accumulated (Bannister, Min. Mag. 25-459; Orcel, Hénin, and Cailliére, M.A. 11-210; Orcel, Cailliére, and Hénin, Min. Mag. 29-331; Brindley, M.A. 11-104 and Min. Mag. 29-502) leads to the conclusion that they are distinct minerals. Chamosite is an oxidized chlorite (Min. Mag. 30-279), while berthierine is structurally allied to eronstedtite, amesite, and the kaolin family. The names ‘kaolin-type ehamosite' and ‘K-type chamosite’ have been used as provisional names for berthierine before the true nature of the Hayanges mineral was established.