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.
CU Online earned through traditional on-campus courses; even if a student completes an entire program online, the degree is awarded with the same benefactor, University of Colorado. CU Online offers courses in liberal arts and science, arts and media, business, education, engineering, public affairs, and architecture and planning. Below are the complete degree programs and certificates that can be completed exclusively through online courses. CU Online CU Online is one of the first fully accredited online education programs, created in 1996 by the University of Colorado Denver (CU Denver). With CU Online, the pedagogy of CU Denver faculty has been extended globally,