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Formula: ScTaO4
Oxide, wolframite group,
columbite supergroup,
scandium- and tantalum-
bearing mineral
Crystal System: Monoclinic
Specific gravity: 6.44 calculated
Hardness: 4½
Streak: Dark brownish (with a reddish hue)
Colour: Very dark brown (to greenish brown in part)
Environments
Heftetjernite was approved in 2006, but to date (August 2024) it has been reported only from the type
locality.
Localities
At the type locality, the Heftetjern pegmatite, Tørdal, Drangedal, Telemark, Norway, heftetjernite occurs as
minute, elongate tabular, very dark brown crystals in a single small void in
albite. Other associated minerals are
fluorite, muscovite, altered
milarite, a metamict, dark greyish brown mineral of the
pyrochlore supergroup, and an unidentified, orange-brown,
tabular, titanium - yttrium -
tantalum - niobium mineral
(EJM 22.2.309-316).
The assemblage occurs in vugs in albite in the mixed LCT
(lithium, cesium,
tantalum)-NYF (niobium,
yttrium, fluorine) type
cleavelandite-amazonite
pegmatite
(HOM).
Heftetjernite from the Heftetjern Pegmatite -
Image
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