Multiple oxide, cervantite group, a bismuth and tantalum bearing mineral
Specific gravity: 8.15 to 8.89
Hardness: 5 to 5½
Streak: Yellowish brown
Colour: Light brown to pitch-black, light smoke-grey to colourless in transmitted light
Solubility: Insoluble in acids
Common impurities: Fe,Mn,Sb,Si,Zn
At the Manuel Balduino claim, Junco do Seridó, Borborema mineral province, Paraíba, Brazil, bismutotantalite occurs as fine large crystals with "bismutomicrolite" (Dana).
At Acari, Rio Grande do Norte, Brazil, bismutotantalite occurs as a placer mineral over a rather wide area, with pebbles found in the beds of several streams many kilometers apart (AM 42.178-183).
At the type locality, Gamba Hill, Busiro county, Wakiso, Central Region, Uganda, bismutotantalite occurs in a granite pegmatite in rough masses or crystals up to several pounds in weight. Associated minerals include schorl, muscovite and cassiterite (AM 15.201, Dana, Mindat, HOM).
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