Yellow crystal aggregates of the rare Bi-Ta mineral bismutotantalite from New Mexico (Harding Mine, Picuris, Taos County, New Mexico, United States of America). Very rich specimen! Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Bismutotantalite
A rare bismuth-tantalum oxide notable for its very high density and refractive index.
Intro adapted from Wikipedia (CC BY-SA).
Bismutotantalite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula BiTaO₄.
It crystallizes in the orthorhombic crystal system (space group Pcnn).
Key properties: Mohs hardness 5–5.5; specific gravity 8.15–8.89; Yellow, yellow-brown to black streak; Adamantine to submetallic luster; optically biaxial.
IMA symbol Bttl, grandfathered status — known before the IMA’s founding, named in 1929.
Found in granite pegmatite (Uganda and Mozambique); as stream-rounded pebbles (Acari, Brazil).
It is found associated with Muscovite, schorl, cassiterite (Gamba Hill, Uganda).
The name refers to BISMuth in its composition, and relation to tantalite.