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.
The Cu Bird Cu bird is dressed, it flies to better lands, and the other birds blame the hoot owl. This is why the latter calls at night to the Cu bird, "Ticú-ticú", and why it cannot see during the day. There is a song titled "El pájaro cu" in the Mexican Son Jarocho style. According to one source, "pájaro cu" is a name used in the Yucatan Peninsula for the russet-crowned motmot, a colorful bird. The Cu Bird The Cu bird (Spanish: "pájaro cu" or "cú") is a bird from a Mexican folktale that is unhappy with its looks. According to the