Cyclosilicates

Cyclosilicates

A member of the tourmaline group of minerals, tourmaline was "discovered" in the early 1800s that some of the "zircons" arriving in European gem centers from the far east were actually a previously undescribed mineral. This mineral can be identified by its hexagonal crystals and hardness. Famous localities for the occurrence of gem varieties include Minas Gerais, Brazil, Ural Mountain, and Madagascar.

Cordierite was named after Pierre Louis A. Cordier (1777-1861), a French mining engineer and geologist, who first studied the species. This mineral commonly alters to some form of mica. It is found as an accessory mineral in granite, gneiss, schists, and in contact metamorphic zones. The transparent variety has been used as a gem known by jewelers as saphir d'eau.

A very minor copper ore, chrysocolla’s name was first used by Theophrastus in 315 BC and comes from the Greek chrysos meaning "gold" and kola meaning "glue," in allusion to the name of the material used to solder gold. This mineral is typically found as glassy botryoidal, rounded masses, or bubbly crusts in green, bluish-green, and blue colors. It can be confused with turquoise but can be distinguished from it by seeing if it sticks to your tongue.

Readily identified by its hexagonal crystals, this mineral is commonly found in pegmatites. It was named after the Greek beryl, which referred to a number of blue-green stones in antiquity. The largest beryl crystal reported (unconfirmed) was 18 m long and 3.5 m wide from Malakialina, Madagascar.

This mineral was named from the Greek word meaning "axe", in allusion to the common habit of its crystals and the iron in the formula. It is found in low to high grade regionally-metamorphosed rocks, contact metamorphic rocks, and pegmatites.

The cyclosilicates form chains as in the inosilicates except that the chains link back around on themselves to form rings. The rings can be made from a minimum of three tetrahedrons up to eight membered rings. The symmetry of the rings is reflected in the symmetry of the minerals.

There are several gemstones in this subclass which is due to the general high hardness, luster, and durability of the minerals.