Wiktionary
boltwoodite
n. (context mineral English) A monoclinic-sphenoidal mineral containing hydrogen, oxygen, potassium, silicon, and uranium.
Wikipedia
Boltwoodite
Boltwoodite is a hydrated potassium uranyl silicate mineral with formula HK(UO)(SiO)ยท1.5(HO). It is formed from the oxidation and alteration of primary uranium ores. It takes the form of a crust on some sandstones that bear uranium. These crusts tend to be yellowish with a silky or vitreous luster.