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Formula: Mg(UO2)(SO4)2.11H2O
Hydrated sulphate, uranyl mineral
Crystal System: Monoclinic
Specific gravity: 2.463 calculated for the empirical formula and 2.434 calculated for the ideal formula
Hardness: 2
Streak: White
Colour: Pale green-yellow
Luminescence: Not fluorescent under UV
Solubility: Easily soluble in water at room-temperature and dehydrates readily even at moderate relative humidity
RADIOACTIVE
Environments
Sedimentary environments
Hydrothermal environments
Localities
At the type locality, the Markey Mine, Red Canyon Mining District, San Juan County, Utah, USA,
magnesioleydetite was found underground. The Markey mine is also a type locality for
feynmanite, leószilárdite
and markeyite. Mineralised channels are in medium- to coarse- grained
sandstone,
conglomeratic
sandstone beds and thick
siltstone lenses. Ore minerals were deposited as replacements of
wood and other organic material and as disseminations in the enclosing
sandstone. Since the mines closed, oxidation of
primary ores in the humid underground environment has produced
a variety of secondary minerals, mainly sulphates, as
efflorescent crusts on the surfaces of mine walls.
Magnesioleydetite and straβmannite are both rare minerals. At
the Markey mine, they are found together on bitumen in association with
arsenuranospathite,
gypsum, metakahlerite,
nováčekite-II, uramarsite and
at least one additional potentially new Mg uranyl sulphate.
These minerals form at ambient temperature by evaporative processes at the surface of a rock with high relative
porosity. The environment is relatively oxidising (high Eh) and solutions are generally acidic (low pH).
Magnesioleydetite occurs as transparent to translucent, pale green–yellow blades up to ∼0.2 mm long, commonly
growing in irregular aggregates to ∼0.5 mm across
(MM 83.3.349-360).
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