Galena of Missouri and Wisconsin; the former mining communities of Galena, Kansas and Galena, Illinois take their names from deposits of this mineral. The largest documented crystal of galena is composite cubo-octahedra from the Great Laxey Mine, Isle of Man, measuring . Galena belongs to the octahedral sulfide group of minerals that have metal ions in octahedral positions, such as the iron sulfide pyrrhotite and the nickel arsenide niccolite. The galena group is named after its most common member, with other isometric members that include manganese bearing alabandite and niningerite. Divalent lead (Pb) cations and sulfur (S) anions form a close-packed
Mineral ore of zinc, or cassiterite (SnO), an ore of tin. Gems are minerals with an ornamental value, and are distinguished from non-gems by their beauty, durability, and usually, rarity. There are about 20 mineral species that qualify as gem minerals, which constitute about 35 of the most common gemstones. Gem minerals are often present in several varieties, and so one mineral can account for several different gemstones; for example, ruby and sapphire are both corundum, AlO. Minerals are classified by variety, species, series and group, in order of increasing generality. The basic level of definition is that of mineral species,