Polytypism of heterogenite

Abstract

SummaryA new variety of heterogenite was found in samples from Mindigi, Shaba, Zaïre. Photometric reflectance varies from 0·235 to 0·165 at λ 5890 Å in air. The bireflectance is 0·070, the degree of anisotropy is 0·7 and the main index in air is 2·7. A thermal weight-loss curve and a microprobe analysis are given and discussed, indicating the formula (Co,Ni) O.OH.The new variety, referred to as heterogenite-H, is hexagonal with cell dimensions a 2·85, c 8·80, space group P63/mmc and cell-content 2 [(Co, Ni)O.OH)]. Indexed X-ray powder data are given. A crystal structure is suggested based on CoO.OH octahedra layers and indicating a polytypic relation between heterogenite-H, the 2H form, and normal heterogenite, the 3R form.