How is slate formed? – Slateplate
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How is slate formed?

How is Slate formed?

Slate is formed by a metamorphosis of clay, shale and volcanic ash that results to a fine-grained foliated rock, resulting in unique slate textures. It is a metamorphic rock, being the finest grained foliated of its kind. It is composed mainly of the minerals quartz and muscovite or illite, often along with biotite, chlorite, hematite and pyrite and less frequently, graphite, kaolinite, magnetite, tourmaline, or zircon as well as feldspar.

More information on Quartz

Quartz, as one of the compositions that build up the slate, is a mineral comprised of silicon and oxygen. Being one of the most-well known minerals on earth, it occurs in basically in all mineral environment and is the important constituents of many rocks. Quartz is also varied from other minerals for it appears in several forms, habits, and colors. Varieties of quartz are usually known as gemstones and are normally used in making jewelry and carvings in hardstone. Quartz is also a useful mineral because of its physical and chemical properties. Quartz can also be valuable because of its electrical properties and heat resistance that can adhere to the nature of electrical products. It is very durable because its hardness reaches 7 in Mohs Scale. Quartz is used in glass making, used as an abrasive, also as a foundry sand and used in the petroleum industry because of its high resistance of being crushed that holds the fracture in facilitating natural glass flow.

Minerals in Slate and their uses

Known as mica, isinglass, or potash mica, Muscovite, a mineral composition of Slate, is a mineral mixture of aluminum and potassium which is complexly hydrated phyllosilicate. It is present in igneous, metamorphic, and sedimentary rocks which are an important rock-forming mineral. It is natural to its existence that it readily cleaves into thin transparent sheets. This mineral can be easily identified because it can be easily split into thin, flexible, colorless, transparent sheets since it has a characteristic of perfect cleavage. Muscovite is also used as one of the minerals used in various products such as pigment in paints, an agent in absorbing sound and vibration in plastics, anti-sticking agent in rubber and its pearly luster in cosmetic products.

More information on Illite

Also, Illite, a Muscovite clay mineral in mica group, is one of the minerals found in Slate which does not expand on absorption of water. It's natural chemical structure, having spaces between individual clay crystal, is responsible for its absence of swelling. It is a crystalline mineral with slightly more silicon, magnesium, iron, and water. Illite is also used for making traditional ceramics. Some minerals are added produce porcelain stoneware tiles.


Biotite, a black mica mineral group, is also formed through a metamorphosis when argillaceous rocks exposed to heat and pressure to form schist and gneiss. This mineral is sometimes found in sediments and sandstones. Chlorite is a mineral that forms during the early stage of metamorphism and usually green in color. Hematite is an important ore of iron and a pigment mineral. It is used in the production of heavy media separation, radiation shielding, and other products. And Pyrite, a mineral that forms at a high and low temperature and occurs in small quantities in any rock formation.


These minerals are known that comprises Slate. Because of these natural compound minerals, it makes Slate widely used for its durability and toughness. Sleekness and aesthetic appearance of Slate made it already a plus and eventually gives an impression of class.