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Formula: Mg[U5+(U6+O2)2O4F3].4H2O
Oxide, uranyl mineral, one of very few minerals with pentavalent
uranium, U5+
Crystal System: Monoclinic
Colour: Deep violet-brown
Luminescence: Non-fluorescent under long wave and short wave UV
RADIOACTIVE
Environments
Sedimentary environments
Hydrothermal environments
Nollmotzite is a relatively new mineral, approved in 2018 and to date (June 2023) reported only from the
type locality. It is one of the very few mineral species with pentavalent uranium U5+, others are
richetite, wyartite, and
shinkolobweite. It is the first natural
uranium oxide containing
fluorine that has been found.
Localities
At the type locality, the Clara mine, Oberwolfach, Wolfach, Ortenaukreis, Freiburg Region, Baden-Württemberg,
Germany, nollmotzite occurs in cavities in quartz
gangue with abundant dark violet to black
fluorite and baryte. It forms deep
violet-brown thin prisms up to ~0.3 mm, with chisel-like terminations.
The presence of fluorine and pentavalent uranium in the structure of
nollmotzite has potentially important
implications for the safe disposal of nuclear waste
(AM 106.163).
Nollmotzite is formed by precipitation from uranium-bearing aqueous
solutions under partially reducing
conditions, most probably enhanced by consumption of oxygen during the oxidation of abundant
pyrite present in the gangue
(HOM).
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