Wiktionary
demesmaekerite
n. (context mineral English) A triclinic-pinacoidal mineral containing copper, hydrogen, lead, oxygen, selenium, and uranium.
Wikipedia
Demesmaekerite
Demesmaekerite is an uranium mineral with the chemical formula: PbCu(UO)(SeO)(OH)•2HO.
It is named after the Belgian mineralogist, who worked at the Musonoi Mine, Gaston Demesmaeker (born 1911). It is a secondary mineral which contains lead, copper and (the rarer in minerals) selenium, it is a bottle green to brown/yellow colour, its crystal habit changes from one form to another form depending on where it is found. It has a Mohs hardness of about 2-3.
It can be found alongside other very rare selenium-bearing uranium ores, such as haynesite, guilleminite, marthozite and piretite.