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.
Lacul cu Nămol Lacul cu Nămol Lacul cu Nămol, also called (Lacul) Balta cu Nămol, is a natural salt lake in the town of Ocna Sibiului, Sibiu County, Transylvania, Romania. It is one of the many lakes of the Ocna Sibiului mine, a large salt mine which has one of the largest salt reserves in Romania. In Romanian, "Lacul cu Nămol" means "the Lake with Mud" . The other name of the lake, Balta cu Nămol, means the Pond with Mud. The lake was formed after an excavation of the salt's cover. Lacul cu Nămol and Lacul Negru are the only lakes of