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Formula: NaCa3(UO2)(CO3)3(SeO3)F(H2O)6
Valence: NaCa3(U6+O2)(CO3)3(Se4+O3)F(H2O)6
Uranyl carbonate-selenite
Crystal system: Trigonal
Specific gravity: 3.16 measured, 3.17 calculated
Hardness: 2 to 3
Streak: Pale yellow-green
Colour: Yellow-green
Luminescence: Fluoresces dimly green under long wave UV and 405 nm illumination but does not fluoresce under short wave UV
Environments
Sedimentary environments
Hydrothermal environments
Szilagyiite is a new mineral, approved in 2024 and to date (May 2026) reported only from the type locality
Localities
The type locality, the Pickett Corral Mine, Montrose County, Colorado, USA, is an inactive
uranium and vanadium mine in the Uravan mineral
belt of the Colorado Plateau. The mine is notable as the type locality for several rare
vanadate minerals including
pseudodickthomssenite, bicapite
and trebiskyite. These vanadates each
occurred in distinct assemblages from that bearing szilagyiite, which is the first
uranium-bearing type species for the locality. In the
sandstone-hosted mine, uranium is
primarily present as uraninite or coffinite,
while vanadium occurs predominantly as
montroseite and corvusite, or in sheet
silicates such as vanadian clays or
roscoelite.
The original uranium and vanadium ores were
deposited when metal-laden groundwater encountered reducing conditions in the presence of abundant organic matter
(asphaltite). In most cases, the strongest
secondary mineralisation occurs intimately within
asphaltite layers and pods. Post-mining oxidation has produced highly diverse
secondary mineralisation throughout the Picket Corral mine due to ongoing
dissolution and recrystallisation. High CO2 content, resulting from decomposition of
calcite by acidic waters derived from decaying sulphides, coupled with periods of high
humidity were likely necessary for the formation of szilagyiite. The szilagyiite occurs in association with
andersonite, schröckingerite, crusts
of magselite and a potentially new Na–Ca-uranyl carbonate-selenite-sulfate with a
complex structure related to szilagyiite and schröckingerite. Material
containing szilagyiite was extracted from a small (~0.25 m)
asphaltite-laden sandstone lens
richly coated by andersonite with sparse but dense patches of fine-grained
ferroselite. The source of Se in szilagyiite is clearly oxidised
ferroselite, given its close association within several centimeters.
Szilagyiite occurs as dense yellow-green rosettes up to 1 mm wide and subparallel tablets up to ~200 µm in size, with
frequent twinning by inversion and one perfect cleavage. It has a pale yellow-green streak and the crystals are transparent with
vitreous lustre and a brittle, uneven fracture
(Journal of Geosciences 70.3.177-188).
Szilagyiite from the Pickett Corral Mine -
Image
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