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Formula: (Nb5+0.5Fe3+0.5)O2
Oxide of niobium and iron,
ixiolite group,
columbite supergroup
Crystal system: Orthorhombic
Specific gravity: 5.033 calculated
Hardness: 5
Streak: Black
Colour: Black
Environments
Nioboixiolite-(Fe3+) is a new mineral, approved in 2024 and to date (December 2025) reported only
from the type locality.
Localities
At the type locality, the In den Dellen quarries, Mendig, Mendig, Mayen-Koblenz, Rhineland-Palatinate, Germany,
nioboixiolite-(Fe3+) was discovered in nosean
"sanidinite" (volcanic rock rich in sanidine) of the Laach Lake volcano. The
associated minerals are
sanidine, K-bearing albite,
nosean, biotite, Nb-rich
ilmenite, Ti-rich magnetite,
hercynite, corundum,
samarskite-(Y), ekebergite
and columbite-(Fe). Nioboixiolite-(Fe3+) forms long
prismatic crystals up to 0.03 × 0.06 × 1 mm3 and epitaxial intergrowths with
ilmenite and intermediate members of the
samarskite–ekebergite series.
Both colour and streak are black and the lustre is submetallic
(MM 89.5.602-608).
Nioboixiolite-(Fe3+) from the In
den Dellen quarries - Image
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