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Slate Formation

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering. Slate is frequently grey in colour, slate occurs in a variety of colours even from a single locality. Slate from North Wales can be found in many shades of grey from pale to dark and may also be purple, green or cyan.

Slate forms when shale, which consists of clay minerals, is put under pressure with temperatures of a few hundred degrees or so. Then the clays begin to revert to the mica minerals from which they formed. This does two things: (1) the rock grows hard enough to ring or "tink" under the hammer, (2) the rock gets a pronounced cleavage direction, so that it breaks along flat planes. Slate cleavage is not always in the same direction as the original sedimentary bedding planes, so any fossils originally in the rock are usually erased, but sometimes they survive in smeared or stretched form. With further metamorphism, slate turns to phyllite, then schist or gneiss.

Slate is usually dark, but it can be colourful too. High-quality slate is an excellent paving stone as well as the material of long-lasting slate roof tiles, floor tiles and the best billiard tables. Blackboards and handheld writing tablets were once made of slate, and the name of the rock has become the name of the tablets themselves, slate.

Chemical composition

Slate is mainly composed of quartz (there are many different varieties of quartz, several of which are semi-precious gemstones. In Europe and the Middle East, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carvings).and muscovite or illite, often along with biotite, chlorite, hematite, and pyrite and, less frequently, apatite, graphite, kaolin, magnetite, tourmaline, or zircon as well as feldspar. Occasionally, as in the purple slates of North Wales, ferrous reduction spheres form around iron nuclei, leaving a light green spotted texture. These spheres are sometimes deformed by a subsequent applied stress field to ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen.

Uses of slate in buildings and interiors.

Slate can be made into roofing slates, also called roofing shingles, installed by a slater. Slate has two lines of breakability: cleavage and grain, which make it possible to split the stone into thin sheets. When broken, slate retains a natural appearance while remaining relatively flat and easily stackable.

Slate flooring  tiles are often used for interior and exterior flooring, stairs, walkways, and wall cladding. Tiles are installed and set on mortar and grouted along the edges. Chemical sealants are often used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence, and increase or reduce surface smoothness. Absolute Tile Care clean and Re-seal and bring back to life your Slate floor tiles. Click here for Care shop for Slate tile care products. Slate tiles are often sold gauged, meaning that the back surface is ground for ease of installation.

Slate flooring can however be slippery when used in external locations subject to rain. Slate tiles were used in 19th century UK building construction and in slate quarrying areas such as Bethesda, Wales there are still many buildings wholly constructed of slate. Slates can also be set into walls to provide a damp-proof membrane. Small off cuts are used as shims to level floor joists. In areas where slate is plentiful it is also used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone. Fine slate can also be used as a whetstone to hone knives. Fireplaces and hearths are made out of slate.

Slate is often used as a decor in freshwater aquariums. Slate will not alter the chemistry of water except in the slate containing feldspar which may leach silicates into the water resulting in excess diatom growth in marine aquaria. Slate is used in some desert reptile enclosures because it holds heat very well.

For your slate floor tile maintenance and care please call Absolute Tile Care 07962 532 526


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