How is slate formed?

Slate is a strong and beautiful natural material that can be used for a variety of purposes around the home.

Most of the slate in the world is mined in order to be made into roof tiles due to its durability and excellent weather resistance. Slate is also popularly used indoors as floor and wall tiles and outdoors as patio tiles.

The slate in our homes may look beautiful, new and polished, but it actually began to form hundreds of millions of years ago.

Composition of slate

Slate is a fine-grained metamorphic rock that is formed through the layering of metamorphic rocks, particularly shale and mudstone. Shale is derived from a sedimentary rock made up from clay or volcanic ash.

During the formation of slate, clay mineral alters into micas. Slate can also contain a significant amount of quartz and some calcite, pyrite and hematite.

Formation of slate

Slate is formed when shale and mudstone are compressed by horizontal forces and low heat. It usually forms in basins between convergent plate boundaries.

Foliation then occurs at right angles to the forces, causing layers of fine-grained clay flakes to regrow perpendicular to the compression.

Because of its unusual perpendicular formation, slate can be cut from the rock in sheets, ideal for building purposes.

Shades of slate

Most slate forms in varying shades of grey, but it is also possible to obtain slate in other colours including shades of grey, purple, red, black, brown and green. The colour of the slate is determined by its mineral composition.

Slate is produced in areas all around the world, but the highest quality of slate can be found in Wales and Brazil.

Find out more about the Welsh slate that we stock here at All Slates by giving our team a call on 01829 262 600.

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