Schoepite

Schoepite, empirical formula (UO₂)₈O₂(OH)₁₂·12(H₂O)^[2] 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.^[2]

Schoepite
General
Category	Uranium minerals
Formula (repeating unit)	(UO2)8O2(OH)12 • 12(H2O)
IMA symbol	Sho[1]
Strunz classification	4.GA.05
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	P21ca
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
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
Other characteristics	Radioactive
References	[2][3][4]

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 Belgian Congo in 1923,^[2] several additional localities are known.

Schoepite was named to honor Alfred Schoep (1881–1966), Professor of Mineralogy at the University of Ghent, Belgium.^[3]

References

1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. Mindat.org
3. Webmineral data
4. Handbook of Mineralogy