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
Streak: Not given.
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.