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September-October 2015

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Who's Who in Mineral Names: David London (b. 1953)

David London (b. 1953)

Londonite, (Cs,K,Rb)Al4Be4(B,Be)12O28, is the cesium-dominant analogue of rhodizite. It was named in honor of David London, professor of geology and geophysics at the University of Oklahoma, in recognition of his experimental studies of evolved granitic melts and his contributions to our understanding of the origin of granitic pegmatites (Simmons et al. 2001). It was discovered in the inner zones and in miarolitic cavities in highly evolved pegmatites rich in red tourmaline at Antandrokomby in the Manandona Valley, Antsirabe region, and at Ampanivana and Antsogombato in the Betafo region south of Mahaiza in Madagascar. It occurs with rhodizite, microcline, quartz, albite, elbaite-liddicoatite-schorl tourmaline, cesium-rich beryl, spodumene, schiavinatoite, danburite, manganese-rich fluorapatite, hambergite, microlite, manganocolumbite, manganotantalite, béhierite, and hafnium-rich zircon. Equant isometric crystals range from a few millimeters to 8 cm and are colorless, white, yellow, and butterscotch-colored. Most crystals are dominated by the dodecahedron, modified by the tristetrahedron, tetrahedron, and cube. Londonite is relatively hard (8 on the Mohs scale), has no cleavage or parting, and has a conchoidal fracture; it also has a high refractive index (1.69) and density (3.42), all of which makes it highly insoluble—unusual for a borate.

Steven C. Chamberlain, a consulting editor of Rocks & Minerals, is an avid collector and researcher specializing in the minerals of New York State.       

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