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Magnesium-zinc-spinels from Ceylon

Published online by Cambridge University Press:  14 March 2018

B. W. Anderson  and
C. J. Payne
B. W. Anderson
Affiliation:
Laboratory of the Diamond, Pearl, and Precious Stone Trade Section of the London Chamber of Commerce
C. J. Payne
Affiliation:
Laboratory of the Diamond, Pearl, and Precious Stone Trade Section of the London Chamber of Commerce
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Extract

Although the mineral spinel belongs to an isomorphous group, and in the simple formula MgO.Al2O3 a both Mg and A1 are susceptible to isomorphous replacement, yet in the transparent varieties oI gem quality there is, as a rule, very little deviation from the type composition, and the physical properties are moderately constant. In fact, one may say that the only considerable replacement hitherto recorded in spinels used as gemstones is by ferrous iron in the variety known as ceylonite or pleonaste, which is black and opaque even when 7 or 8 % of FeO is present, the end-member of this series being hercynite, FeO.Al2O3, with 41% ferrous oxide.

The purpose of this paper is to draw attention to certain transparent blue spinels from the gem gravels of Ceylon, the physical properties of which differ quite strikingly from those of the normal spinels, from which they are indistinguishable in appearance, magnesium being replaced in this instance not by ferrous iron but by zinc.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 24 , Issue 158 , September 1937 , pp. 547 - 554
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1937

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References

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Page 551 note 1 Based on Goldschmidt's, V. M. X-ray measurements of the cell side for ZnO.Al2O3, 8.062, and MgO.Al2O3, 8.059Å. (Zeits. Physikal. Chem., Abt. B, 1932, vol. 18. p. 29)Google Scholar, and taking the density of MgO.A12O3 as 3.585. Refractive index as quoted by E. S. Larsen for artificial gahnite (Microscopic determination of the nonopaque minerals, Bull. U.S. Geol. Surv., 1934, no. 848, p. 58).

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