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Microlite

Microlite was once known as a pale-yellow, reddish-brown, or black isometric mineral composed of sodium calcium tantalum oxide with a small amount of fluorine. Its chemical formula is (Na,Ca)2Ta2O6(O,OH,F). Today it is a name of a group of oxide minerals of a similar stoichiometry having tantalum prevailing over titanium and niobium. The microlite group belongs to a large pyrochlore supergroup that occurs in pegmatites and constitutes an ore of tantalum. It has a Mohs hardness of 5.5 and a variable specific gravity of 4.2 to 6.4. It occurs as disseminated microscopic subtranslucent to opaque octahedral crystals with a refractive index of 2.0 to 2.2. Microlite is also called djalmaite, but both names are now obsolete.

Additional reading
• Andrade, M. B., Atencio, D., Menezes Filho, L. A., & Ellena, J. (2011). The crystal structure of a microlite-group mineral with a formula near NaCaTa2O6F from the Morro Redondo mine, Coronel Murta, Minas Gerais, Brazil (vol 49, pg 615, 2011). Canadian Mineralogist, 49(5), 1338–1338.*Atencio, D., Andrade, M. B., Christy, A. G., Gieré, R., & Kartashov, P. M. (2010). The pyrochlore supergroup of minerals: nomenclature. The Canadian Mineralogist, 48(3), 673–698.[https://pubs.geoscienceworld.org/canmin/article-abstract/48/3/673/127162/THE-PYROCHLORE-SUPERGROUP-OF-MINERALS-NOMENCLATURE • • • Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy, (7th edition), v. I, 748–757
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