Schoepite

Schoepite
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General
Category	Uranium minerals
Formula (repeating unit)	(UO2)8O2(OH)12 • 12(H2O)
Strunz classification	4.GA.05
Crystal symmetry	Orthorhombic - pyramidal H-M symbol (mm2) Space group: P 21ca
Unit cell	a = 14.33 Å, b = 16.79 Å c = 14.73 Å; Z = 4
Identification
Color	Amber, lemon- or sulfur yellow
Crystal habit	Commonly as tabular equant, to short prismatic crystals; rarely in microcrystalline aggregates
Crystal system	Orthorhombic
Cleavage	[001] Perfect, [010] indistinct
Tenacity	Brittle
Mohs scale hardness	2.5
Luster	Adamantine
Streak	Yellow
Diaphaneity	Transparent to translucent
Specific gravity	4.8
Optical properties	Biaxial (-)
Refractive index	nα = 1.690 nβ = 1.714 nγ = 1.735
Birefringence	δ = 0.045
Pleochroism	X = almost colorless; Y = Z = lemon-yellow to golden yellow
2V angle	Measured: 89°
Ultraviolet fluorescence	Short and long UV = pale green
References

Schoepite, empirical formula (UO₂)₈O₂(OH)₁₂•12(H₂O) is a rare alteration product of uraninite in hydrothermal uranium deposits. It may also form directly from ianthinite. The mineral presents as a transparent to translucent yellow, lemon yellow, brownish yellow, or amber orthorhombic tabular crystals. Although over 20 other crystal forms have been noted; rarely in microcrystalline aggregates. When exposed to air schoepite converts over a short time to the metaschoepite form (UO₃ • nH₂O, n < 2) within a few months of being exposed to ambient air.

The hardness is 2.5, density is 4.8 g/cm³, and it streaks yellow.

It was first described from specimens from Shinkolobwe mine in Zaïre in 1923, several additional localities are known.

Schoepite was named to honor Alfred Schoep (1881–1966), Professor of Mineralogy at the University of Ghent, Belgium.