Slate is a fine grain, metamorphic flagstone that is mostly made up of minerals or micas, depending on the level of metamorphism that it is exposed to. It naturally comes in various shades of gray, as well as some shades of green, black, purple, brown, and red, dependent on the amount and types of organic material and iron. The stone can also contain small amounts of quartz and other minerals such as calcite, feldspar, hematite, and pyrite. Though slate was often referred to as shale, it is important to remember that they are not the same since shale is a stone that is progressively turned into slate. This stone has stored energy that make it durable and resistant to fire, frost, and cracking due to freezing. Slate can patina over time as it oxidizes while being exposed to elements such as water and air.

When sedimentary rock basins are compressed and exposed to even minor forms of heat, they will form slate. The minerals and micas melt together within the basins and create repetitive slate layers within the cracks. This process is also referred to as vertical foliation. The slate is then obtained through breaks in the stone and extracted. The stone is cut, finished, chiseled, and shaped according to its desired end use. Slate is a popular stone to use for roofing and exterior paving, as well as dimensional decorative stones, tabletops, chalkboards, interior flooring, monuments, wall cladding, and decorative aggregate.


Related Terms

Was this insightful?