Group 12 element zinc and cadmium which makes geological separation unlikely. As a consequence, cadmium is produced mainly as a byproduct from mining, smelting, and refining sulfidic ores of zinc, and, to a lesser degree, lead and copper. One place where metallic cadmium can be found is the Vilyuy River basin in Siberia. Although mercury is an extremely rare element in the Earth's crust, because it does not blend geochemically with those elements that constitute the majority of the crustal mass, mercury ores can be highly concentrated considering the element's abundance in ordinary rock. The richest mercury ores contain up to 2.5% mercury
Group 6 element principal ore from which molybdenum is now extracted—was previously known as molybdena, which was confused with and often implemented as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant. Even when molybdena was distinguishable from graphite, it was still confused with a galena (a common lead ore), which took its name from Ancient Greek "", meaning "lead". It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead. He and other chemists then correctly assumed that it was the ore of a