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Bayleyite sample from the Ambrosia Lake area, Grants District, New Mexico (size: 4.6 x 2.4 x 1.6 cm)
Category Carbonate mineral
(repeating unit)
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
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 [1][2][3]

Bayleyite is an 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.[1]


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.[3]