Zinc-bearing chromite (donathite?) from Norway: a second look
SUMMARY. Electron-microprobe analyses of chromites from the Helgeland area, Norway, show that they are all low in zinc. Many chromites show physical properties identical with donathite (anisotropism; polar magnetism) but have cubic lattices. One exception, from Rodoya, shows an unusual deviation fro...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.624.6161 http://www.minersoc.org/pages/Archive-MM/Volume_41/41-319-351.pdf |
| Summary: | SUMMARY. Electron-microprobe analyses of chromites from the Helgeland area, Norway, show that they are all low in zinc. Many chromites show physical properties identical with donathite (anisotropism; polar magnetism) but have cubic lattices. One exception, from Rodoya, shows an unusual deviation from cubic symmetry and that there may exist complex intergrowths oftwo different tetragonal lattices and a cubic lattice. The similarity between the chromites tudied and donathite suggests hat the chemistry and crystallography of that mineral may be more complex than is currently accepted. DONATH (I93I) reported that chromites from Ramberget, Hestmona ( = Hestmann~y) and V~ernes, in the north Helgeland area of west Norway, contained zinc as a major component. This report, which included two analyses of chromites with ZnO contents of 2.62 and 2.2I ~o, has since been referred to in a number of standard textbooks on mineralogy and in recent publications (Thayer et al., 1964; Weiser, I967). Seeliger and Miicke (I969) on the basis of these original analyses and their own X-ray powder photographs have defined this as a new mineral, Donathite (see also Fleischer, I969), which they found to be tetragonal with a c/a ratio of o'9956. The mineral is found in a deposit regarded by Donath (193I) as a 'standard type ' and the presence of considerable zinc is all the more surprising since the host ultramafic |
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