Boltwoodite, Hydrogen potassium uranyl silicate, formula HK(UO₂)SiO₄.1.5H₂O).

Crystal system: Monoclinic.(usually forming radial sprays of acicular crystals).
Hardness: 3.5 to 4
Density: 3.6 gms/cm³
Colour: Yellow.
Streak: Not given.

[Strongly Radioactive]

Boltwoodite is formed in silicate zones surrounding uraninite deposits as an alteration product of uraninite (uranium oxide, UO₂). It is found in widely scattered locations having widely differing geology.

The specimen shown in the picture comes from Rossing Mine, Swakopmund, Namibia, South West Africa.