Boltwoodite Locality: Goanikontes Claim, Arandis , Swakopmund District, Erongo Region , Namibia ( Locality at mindat.org ) Size: 1.8 x 1.7 x 1.4 cm. A lovely thumbnail consisting of very fine acicular crystals of umber-yellow boltwoodite. The needles exhibit both a radial growth and a vertical cluster habit not unlike what you see in some palms, and are superb in both color and habit. Tim Blackwood Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Boltwoodite
A hydrated potassium-sodium uranyl silicate — the monoclinic relative of sodium boltwoodite.
Intro adapted from Wikipedia (CC BY-SA).
Boltwoodite is an IMA-recognized mineral species in the silicate class, with the chemical formula (K,Na)(UO₂)(SiO₃OH)·1.5H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 3.5–4; specific gravity 4.7; Pearly; radial aggregates vitreous to silky; dull to earthy in microcrystalline pseudomorphs luster; refractive index 1.688; optically biaxial.
IMA symbol Bwd, grandfathered status — known before the IMA’s founding, named in 1956.
Found in the outer silicate zone of alteration surrounding hydrated uranyl oxides incrusting primary uraninite; also filling fractures at some distance from primary uraninite.
It is found associated with Uraninite, becquerelite, fourmarierite, phosphouranylite, gypsum, fluorite.
The name refers to Bertram Borden Boltwood (1870–1927), radiochemist of Yale University, New Haven, Connecticut, USA, who devised the U{Pb method of measuring geologic time.