betafite

betafite

[′bed·ə‚fīt]
(mineralogy)
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At the Main Show, John was selling specimens showing reasonably sharp, dull brown betafite cuboctahedrons to 3 cm; crystal clusters, with or without matrix, to 7 cm were going for $50 to $150.
Sure enough, from the old biotite and uranium workings known as the Silver Crater mine, near Bancroft, he dug out betafite crystals by the dozen, some equaling the best from the 1950's and 1960's for sharpness and general class.
The crystal groups were found enclosed in muscovite and schorl, and some of their surfaces show brown spots of a radioactive mineral (betafite?).
His big betafite from Madagascar--I haven't seen better.
Included were Madagascar rare-earth classics like sharp betafite crystals to 4 cm; well-composed earthy brown sprays of 2-cm euxenite crystals; swarms of loose 1 and 2-cm cubes of lustrous black thorianite; and allanite crystal groups from Madagascar and from Alto Ligonha, Mozambique.
Behier wrote a mineralogy of Mozambique (1957) and a supplement to the mineralogy of Madagascar (1960); consequently his collection was strong in Madagascar minerals, including tourmaline, betafite, thorianite, and other pegmatite species.
Associations include betafite, euxenite, monazite and xenotime-(Y) (DSGM, 1974).
Betafite [(Ca,Na,U)sub.2][(Ti,Nb,Ta).sub.2][O.sub.6](OH)
Betafite has been reported from the Ile pegmatite, in association with euxenite, allanite and monazite, and from the Ehiale-Namovela-Massive-Horta group in association with euxenite and samarskite (DSGM, 1974).
plumbobetafite, bismutobetafite and betafite) [(Pb, Y, U, Ca).sub.2-x][Nb.sub.2][O.sub.6](OH)
Solid-solution between pyrochlore and betafite is indicated by the microprobe analyses.
Also obtained by exchange from one or several of these localities are many other rare and interesting species such as superb danburite, nosean, afghanite, transparent allanite, tadzhikite-(Ce), green thorite, urano-thorianite, asbecasite, stillwellite-(Ce), transparent brown baddeleyite, tiny red-brown crystals of betafite, very small, dark brown crystals of zirconolite-3T, and beautiful, greenish yellow, transparent crystals of vicanite-Ce.