Microlite

Microlite is a pale-yellow, reddish-brown, or black isometric mineral composed of sodium calcium tantalum oxide with a small amount of fluorine (Na,Ca)₂Ta₂O₆(O,OH,F). Microlite is a mineral in the pyrochlore group 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.

Microlite occurs as a primary mineral in lithium-bearing granite pegmatites, and in miarolitic cavities in granites. Association minerals include: albite, lepidolite, topaz, beryl, tourmaline, spessartine, tantalite and fluorite.

Microlite was first described in 1835 for an occurrence on the Island of Uto, State of Stockholm, Sweden. A type locality is the Clark Ledges pegmatite, Chesterfield, Hampshire County, Massachusetts. The name is from Greek mikros for "small" and lithos for "stone."

References

• Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy, (7th edition), v. I, 748–757
• Webmineral data
• Mindat with location data
• Mineral data publishing PDF

Wikimedia Commons has media related to Microlite.

• 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.doi: 10.3749/canmin.48.3.673
• 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.doi:10.3749/canmin.49.2.615