- Ceylonite
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Ceylonite (first cited 1793) and Pleonaste (first cited 1801) are dingy blue or grey to black varieties of spinel. Ceylonite, apparently named for the island of Ceylon (where it is not known to occur), is a ferroan spinel with Mg:Fe from 3:1 and 1:1, and little or no ferric iron. Pleonaste is named from the Greek for 'abundant,' for its many crystal forms, and is distinguished chemically by low Mg:Fe ratios of approximately 1:3.
Ceylonite and pleonaste are old terms with (apparently) no precise meaning. Nevertheless, both terms are still occasionally used in the current mineralogical literature.
References
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