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Formula: Ca(UO2)(CO3)2.5H2O
Hydrated carbonate, uranyl mineral,
Orthorhombic paramorph of
meyrowitzite
Crystal System: Orthorhombic
Specific gravity: 3.25 measured, 3.242 calculated
Hardness: 2
Streak: White
Colour: Light lemon-yellow
Luminescence: Fluoresces eakly patchy green under both short wave and long wave UV
Very strongly RADIOACTIVE
Environments
Sedimentary environments
Hydrothermal environments
Zellerite is a rare weathering product of uranium ores, formed at low
pH (acid) in the presence of oxidising pyrite. Associated minerals include
metazellerite, gypsum,
limonite, iron sulphides,
schoepite, meta-autunite,
uranophane and opal
(HOM).
Localities
At McKinley County, New Mexico, USA and the Pat No. 8 Occurrence, Southern Powder River Basin Mining District,
Converse County, Wyoming, USA, zellerite occurrences are similar to that at the Lucky MC mine (see below) in
that the zellerite forms as small veins and clumps in oxidised zones surrounding the unoxidized ore
(AM 51.1567-1578).
At the type locality, the Lucky MC mine, Fremont County, Wyoming, USA, zellerite is found as incrustartions on
arkosic country rock; it is formed during surface oxidation of the
uranium ore. The unoxidised ore in the mine is a fine-grained mixture of
uraninite, coffinite and
iron sulphides filling intergranular areas in arkose. The coarse and
porous nature of the host rock allows rapid moist-air oxidation of these
primary uranium
minerals and sulphides. In the early stages of oxidation, black
primary ore commonly contains fine seams of green
liebigite intergrown with gypsum.
Rimming this dark ore is a rusty brown zone where the oxidation has effected the breakdown of all the
primary uranium
minerals and some of the iron sulphides. Zellerite is most commonly present in this zone where it is
associated with gypsum, limonite and
partially altered iron sulphides. It forms extremely fine fibres that aggregate into pincushion clumps.
Schoepite, meta-autunite,
uranophane and uranium-bearing
opal are present in the more intensely oxidised zones contiguous to the
zellerite.
Zellerite crystals are always fibrous and hairlike, aggregating into pincushion clumps. Zellerite is a
light lemon yellow and on dehydration becomes chalky yellow. Individual crystals seldom exceed 2 mm in length and
5 microns in width
(AM 51.1567-1578).
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