The Nature of Garnierites—I Structures, Chemical Compositions and Color Characteristics

G. W. Brindley and Pham Thi Hang
Materials Research Laboratory, and Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania, 16802, U.S.A.

Abstract: X-ray diffraction patterns of garnierites indicate that most samples resemble serpentine-group minerals or a talc-like mineral, or a mixture of these forms, and give respectively 7 Å and 10 Å basal reflections. From a survey of some 40 garnierites, four of predominantly serpentine type and seven of predominantly talc-like type were selected for detailed study. The talc-like garnierites exhibit little variation of the 10 Å basal spacing with low-temperature heating or with immersion in liquids, though some may contain a small proportion of expandable layers. Chemical analyses show considerable deviations of octahedral/tetrahedral cation ratios from the values 3/2 and 3/4 for normal serpentine and talc minerals, and may be interpreted in terms of mixed 1:1 and 2:1 layer types, either as separate phases and/or as interstratifications, or as defect structures of various kinds. The H2O+ contents of the talc-like forms of garnierite are considerably greater than that of normal talc and point to a mineral of composition 3(Mg, Ni)O·4SiO2. 2H2O or [(Mg, Ni)3Si4O10(OH)2]·H2O—a talc monohydrate formula. The green color of garnierites is related to the NiO weight per cent and a color index is derived based on the Munsell color charts.

Clays and Clay Minerals; February 1973 v. 21; no. 1; p. 27-40; DOI: 10.1346/CCMN.1973.0210106
© 1973, The Clay Minerals Society
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