How Slate is Formed
Slate is a fine-grained metamorphic rock consisting primarily of quartz and a mineral combination of aluminum and potassium. When quarried, slate typically forms smooth sheets of stone. Slate is derived from original shale-type sedimentary rock, which is primarily composed of clay or volcanic ash. Shale is a fine-grained combination of flakes of clay and particles of other minerals, such as quartz and calcite. Slate is composed of quartz and muscovite, in addition to deposits of chlorite, hematite and pyrite. Some forms of slate contain traces of feldspar, graphite, magnetite, tourmaline and zircon, all of which contribute to color and texture variations. Slate is formed by the effects of heat and pressure on shale or mudstone rock formations, known as metamorphism. Metamorphic processes vary according to specific geographic locations.
Low-grade regional metamorphism occurs as a result of changes in physical and chemical conditions. Regional metamorphism covers large areas of the earth¹s continental crust, typically associated with mountain ranges. The collision of two continental plates can produce the extreme forces of compression required for the formation of slate.
Contact metamorphism occurs around intrusive igneous rocks. Igneous rocks are formed by the cooling and solidification of lava or magma. The process occurs as a result of temperature increases caused by liquid rock that forms under the earth¹s surface. Magma or lava is slowly forced up to the surface from deep within the earth and settles into cracks and crevices in existing rock formations. As the rock slowly cools into a solid, the remaining particles of magma crystallize, forming the interesting veins and striations found in slate.
Dynamic metamorphism occurs primarily in zones of high strain, such as fault zones adjacent to an active volcano. A violent volcanic eruption can cause a forceful crushing and grinding of rocks into angular fragments. Slate formed in this manner is characterized by a fine-grained matrix and smooth texture.
Mineral, chemical and crystallization changes occur during metamorphism, resulting in variations in color patterns and surface textures. Slate forms smooth sheets of stone with two fracture lines, the cleavage and the grain. When slate is split or broken, the stone retains its natural appearance.
Uses for Slate Slabs and Tiles
Slate tiles are fabricated from large slabs of stone directly from quarries. Due to color veins caused by natural mineral impurities, no slate tile is identical. Tiles can be arranged in patterns or slabs to create an interesting and multi-dimensional residential or commercial floor installation. There are many advantages of slate as opposed to other types of dimension stone. Slate is fireproof and extremely durable, making its ideal for use on the interior and exterior of fireplaces. The mildly textured surface provides a non-slip floor surface, which makes slate perfect for outdoor applications. When used for indoor floor installations, slate tiles maintain a constant floor temperature. Heating or air cooling systems can be installed beneath the tile, creating radiant heat and cooling.
Slate slabs and tiles are virtually indestructible and have a long life span. Slate is crack, chip and scratch resistant, making it a perfect choice for floors in high traffic areas. Slate is versatile, and can be used as kitchen countertops, backsplashes, wall cladding, bathroom applications, fireplace surrounds, wainscoting, crown molding, doors and entryways. Slate is a favored choice for constructing stairs, walkways, driveways and wall cladding. Slate can be used as patio or deck surface flooring and can create interesting outdoor landscaping projects, such as retaining walls, fountains and garden planting areas.
Slate is usually dark gray in color, but is available in natural shades of purple, green and blue. Uses include interior and exterior flooring, wall cladding, fireplace foundations and roofing tiles. Slate is one of the most popular roofing tile materials due to its low water absorption and its natural resistance to damage caused by frost or freezing temperatures.
Sealants may be used to improve the durability and appearance of slate installations, to increase stain resistance and increase or reduce surface smoothness.