Crookesite Crookesite Crookesite is a selenide mineral composed of copper and selenium with variable thallium and silver. Its chemical formula is reported either as Cu(Tl,Ag)Se or (Cu,Tl,Ag)Se. It is formed by precipitation from hydrothermal fluids, and contains by mass: 16.3% Tl, 47.3% Cu, 2.9% Ag, and 33.6% Se. Crookesite is an opaque, bluish grey to pink toned brown metallic mineral crystallizing in the tetragonal system. It has a Mohs hardness of 2.5 to 3 and a specific gravity of 6.9. It was discovered in 1866 in Skrikerum, Sweden and named for Sir William Crookes (1832–1919), the discoverer of the element thallium.
Naming of chemical elements after Amerigo Vespucci The non-transuranic element samarium is named after Vasili Samarsky-Bykhovets, and gadolinium is indirectly named (via the mineral gadolinite), after Johan Gadolin. Lecoq de Boisbaudran, who named the element gallium after his native land of France (from Latin "Gallia" meaning Gaul) denied that the element's naming was for a pun on his own name ("le coq" means "the rooster" in French, as does "gallus" in Latin). Some chemical elements are named after places on the planet earth. Five are named after currently existing countries – polonium (named after Poland), francium and gallium (named after France), nihonium (named after