Phyllosilicates

Phyllosilicates

A “1” on Mohs hardness scale, this mineral can be identified by its softness and greasy feel. It is formed from the hydrothermal alteration of mafic rocks and during low-temperature metamorphism. It is used for laboratory table tops, electric switchboards, and as soapstone. The name comes from the Arabic word for "pure," probably alluding to the color of its powder.

Serpentine is a common and widely distributed mineral which forms as an alteration of magnesium silicates. The variety chrysotile is the chief source of asbestos. It was named from the Greek ophites, meaning “of a serpent.”

A comparatively rare mineral, pyrophyllite is found in metamorphic rocks and was named from the Greek word for "fire" and "leaf" for the way it exfoliates when heated. It is mined and used as low-grade talc.

A widespread member of the mica group, this mineral is characterized by its brownish-red color. It was named from the Greek phlogopos for "resembling fire," in allusion to is red tint. It is found in contact and regional metamorphic rocks and as a common mineral in kimberlite.

The perfect cleavage of this mineral allows it to be split into very thin flexible sheets. It is the most common of the mica group minerals and is typically found occurring as "books." The name was used as early as 1794 by Johann Gottfried Schmeisser in his System of Mineralogy and is derived from the term "Muscovy glass," which was a substitute for glass.

Described by Mohs in 1820, this mica group mineral occurs with corundum. Its name is from the Greek word meaning "pearl."

Known as the "pink mica," this mineral was named in 1792 by Martin Klaproth from the Greek words Lepidos for "scale" and Lithos for "stone." It is a comparatively rare mineral found in pegmatites usually associated with other lithium-bearing minerals. It is a source of lithium and used in the manufacture of heat-resistant glass.

Kaolinite is a common mineral, formed by weathering or hydrothermal alteration of feldspar. Many and varied products are made from this mineral which includes common brick, drain tile, and in high-grade form, china and pottery. Its largest use is as filler in paper. The name is derived from the ancient Chinese locality "Kaoling (Gaoling)," meaning “high ridge.”

This mineral occurs within a great range of compositions and is considered a group. It is characterized by its green color, micaceous habit, and cleavage, but its sheets are not elastic. It is a common mineral formed from alteration during low grade metamorphism. The name is derived from a Greek word meaning "green," in allusion to the common color of the mineral.

The splendent luster and dark sheets of this mineral from the mica group distinguish it from the others in the group. It is one of the rock-forming minerals and is widely distributed in igneous rocks. Vermiculite, which forms as an alteration of biotite, has water molecules interlayered in the sheets. On heating, it loses water and expands into wormlike forms. The mineral was named in honor of the French physicist, J.B. Biot.