Boltwoodite

Formula:  HK(UO₂)SiO₄ ^. 1.5H₂O

Origin of name:  For Bertram Boltwood (1870-1927), radiochemist, Yale University, New Haven, Connecticut, U.S.A., who devised the U-Pb method for measuring geologic time

Crystal system:  Monoclinic

Crystal class:  2

Twinning:

Unit cell: a = 7.07 Ǻ, b = 7.06 Ǻ, c = 6.64 Ǻ, β = 105.8°

Colour:  Pale yellow

Diaphaneity: Transparent to translucent

Luster:  Pearly on cleavage

Habit: Radiating acicular to fibrous

Hardness:  3.5 to 4

Specific gravity:  3.60

Cleavage:  2; {010} perfect, {001} imperfect

Tenacity:

Streak:

Synonyms/varieties:

Comments:  Often fluoresces dull green in both SW- and LW-UV, radioactive. Found in the outer silicate zone of alteration surrounding hydrated uranyl oxides incrusting primary uraninite, also filling fractures at some distance from uraninite. Also found in a pegmatite and Colorado-Plateau type sanstone uranium deposits.