Mineralogy and Crystal Structure of Chamosite

Abstract

THE occurrence of the hydrous ferrous silicate, chamosite, in sedimentary ironstones was described by Hallimond¹. Later, with Harvey and Bannister², he concluded that chamosite differed from the iron-bearing chlorites. Brindley^3,4 examined chamosites from laterites and other sources, and concluded that they were of kaolin-type. Many of the variations in X-ray diagrams were accounted for by the existence of two kaolin-type structures, one ortho-hexagonal and one monoclinic, with simply related cell dimensions. In common with some other clay minerals, chamosite had random displacements of layers parallel to the b-axis of integral multiples of b/3, giving rise to sharp (hkl) reflexions only for k = 3n. Brindley concluded from the presence of (hkl) reflexions for h ≠ 3n that there were no random a-axis displacements of layers within a single structure, similar to the ‘mistakes’ in the cobalt structure of Wilson⁵ and Edwards, Lipson and Wilson⁶. The pure ortho-hexagonal form was found in an iron ore from the main oolitic beds at Corby, Northamptonshire, by Brindley and Youell⁷.