Tourmaline is the name of a group composed of complex lithium borosilicate minerals. Tourmalines have a crystal structure in which many elements can substitute for others. This results in a large group of species with a wide range of chemistry and appearance. The sodium-rich tourmaline called elbaite is the most familiar, because it is the species with the widest range of colors and is the one most typically cut as a gemstone. Crystals are usually pencil-shaped and have a characteristic trigonal (three-fold) symmetry axis. Larger crystals can be more like broad cyllinders and have elongated grooves called striations. Changes in the composition of growth solutions result in color zoning, which can be along the length of a crystal or in layers moving outward from the center and best seen in cross-sections. Reds and greens make elbaite crystals attractive and greatly in demand for gem use. Some tourmalines display many colors, and gemmy crystals up to several feet long are known. Fine tourmalines occur worldwide; gem material is notable from Brazil, California, Malagasay Republic, Nigeria and Afghanistan.