Bayleyite

Bayleyite
Bayleyite sample from the Ambrosia Lake area, Grants District, New Mexico (size: 4.6 × 2.4 × 1.6 cm)
General
Category	Carbonate mineral
Formula (repeating unit)	Mg2(UO2)(CO3)3·18(H2O)
IMA symbol	Byy
Strunz classification	5.ED.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Unit cell	a = 26.65 Å, b = 15.31 Å, c = 6.53 Å; β = 93.07°; Z = 4
Identification
Color	Sulfur yellow
Crystal habit	Clusters of prismatic crystals, crusts
Fracture	Conchoidal
Mohs scale hardness	2–2.5
Luster	Vitreous
Diaphaneity	Semitransparent
Specific gravity	2.05
Optical properties	Biaxial (−)
Refractive index	nα = 1.453 – 1.455 nβ = 1.490 – 1.492 nγ = 1.498 – 1.502
Birefringence	δ = 0.045 – 0.047
Pleochroism	Visible: X = Pinkish, Y = Light yellow, Z = Light yellow
2V angle	Measured: 30°
Ultraviolet fluorescence	Weak; yellow-green to pale greenish under LW and SW
Other characteristics	Radioactive
References

Bayleyite is a uranium carbonate mineral with the chemical formula: Mg₂(UO₂)(CO₃)₃·18(H₂O). It is a secondary mineral which contains magnesium, uranium and carbon. It is a bright yellow color. Its crystal habit is acicular but is more commonly found as crusts on uranium bearing ores. It has a Mohs hardness of about 2–2.5.

Occurrence

It was first described in 1948 for an occurrence in the Hillside mine, north of Bagdad, Yavapai County, Arizona and named for mineralogist William Shirley Bayley (1861–1943) of the University of Illinois. It occurs as an efflorescence or coating on other secondary minerals and often is deposited on mine walls and workings. It occurs with schrockingerite, andersonite, swartzite and gypsum in the Hillside mine; with schrockingerite and gypsum in the Hideout mine in Utah; and with tyuyamunite, uranophane, liebigite and carnotite in the Powder River Basin in Wyoming.