Light pinkish-violet platy crystals of the very rare mineral holtite from Vasin-Myl'k Mountain, Voron'i Tundry, Murmansk Oblast, Russian Federation. Holtite is tantalum oxide mineral. Ex.Dr.Hartel and Ch.Rewitzer collections — Photo: David Hospital · CC BY-SA 4.0
Holtite
Holtite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Ta₀.₆ ₀.₄)Al₆BSi₃O₁₈.
It crystallizes in the orthorhombic crystal system (space group Pnma). It is a member of the Dumortierite structural group.
Key properties: Mohs hardness 8.5; specific gravity 3.6–3.9; Light buff streak; Resinous, vitreous, dull when weathered luster; optically biaxial.
IMA symbol Hlt, IMA status: approved, named in 1969.
Occurs as coatings on stibiotantalite and replacing tantalite in a pegmatite (Greenbushes, Western Australia); in pegmatites cutting amphibolites (Voron'i massif, Russia); in alluvial gravels derived from pegmatite.
It is found associated with Stibiotantalite, tantalite, tourmaline, microlite, quartz (Greenbushes, Western Australia); stibiotantalite, microlite, tantite (Voron'i massif, Russia).
The mineral was named to honor Harold Edward Holt (1908-1967), Prime Minister of Australia (1966-1967).