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Category Silicate mineral
(repeating unit)
Strunz classification 9.AK.30
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Cmmb
Unit cell a = 14.26 Å, b = 35.88 Å
c = 14.2 Å; Z = 16
Colour Yellow
Crystal habit Occurs as acicular to elongated bladed crystals, flattened on {010}, also as radiating fibrous clusters and spherulites, pseudotetragonal
Cleavage Distinct prismatic
Mohs scale hardness 1 - 2
Lustre Waxy to silky
Streak Yellow
Diaphaneity Transparent to translucent
Specific gravity 4.1
Optical properties Biaxial (-)
Refractive index nα = 1.596 nβ = 1.603 nγ = 1.606
Birefringence δ = 0.010
Pleochroism X = colorless; Y = pale yellow-green; Z = yellow-green
2V angle Measured: 60°
Other characteristics Radioactive greater than 70 Bq/g
References [1][2][3]

Weeksite is a naturally occurring uranium silicate mineral with the chemical formula: K2(UO2)2Si6O15•4(H2O), potassium uranyl silicate. Weeksite has a Mohs hardness of 1-2. It was named for USGS mineralogist Alice Mary Dowse Weeks (1909–1988).[2][3]


Weeksite is visually similar to other uranium minerals such as carnotite and zippeite, both being encrustations that form on other rocks (usually sandstones or limestones).


Weeksite was first described in 1960 for an occurrence on Topaz Mountain, Thomas Range, Juab County, Utah.[1]

Weeksite occurs within small "opal" veins within rhyolite and agglomerates, and as encrustations in sandstones and limestones. It occurs associated with opal, chalcedony, calcite, gypsum, fluorite, uraninite, thorogummite, uranophane, boltwoodite, carnotite and margaritasite.[2]


  1. ^ a b "Weeksite mineral information and data". Mindat.org. 2011-06-19. Retrieved 2012-02-10. 
  2. ^ a b c Handbook of Mineralogy
  3. ^ a b Webmineral data for weeksite