Uranium ore support a neutron-mediated chain reaction). Uranium, thorium, and potassium are the main elements contributing to natural terrestrial radioactivity. Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70% denser than lead, but not as dense as tungsten, gold, platinum, iridium, or osmium. It is always found combined with other elements. Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernova explosions. The primary uranium ore mineral is uraninite (UO) (previously known as pitchblende). A range of other uranium minerals can be found in various deposits. These
Stephanite tetrahedrite, galena, sphalerite and pyrite. Localities which have yielded good crystallized specimens are Freiberg and Gersdorf near Rosswein in Saxony, Chañarcillo in Chile, and exceptionally Cornwall. In the Comstock lode in Nevada massive stephanite and argentite are important ores of silver. Stephanite Stephanite is a silver antimony sulfosalt mineral with formula: AgSbS It is composed of 68.8% silver, and sometimes is of importance as an ore of this metal. Under the name Schwarzerz it was mentioned by Georgius Agricola in 1546, and it has been variously known as "black silver ore" (German "Schwarzgultigerz"), brittle silver-ore ("Sprödglanzerz"), etc. The name stephanite