Home Metamorphic Rocks Foliated Metamorphic Rocks Slate

Slate

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Slate is a fine-grained, foliated metamorphic rock this is created via the alteration of shale or mudstone by means of low-grade local metamorphism. It is famous for a extensive form of makes use of such as roofing, floors, and flagging due to its sturdiness and appealing look.

Colour: Variable colour – black, blue, green, red, brown and buff.

Texture – Foliated Metamorphic Rock, Foliation on a mm Scale.

Grain size – Very fine-grained; crystals not visible to the naked eye.

Hardness – Hard and brittle.

Other features – smooth to touch.

Major minerals: Quartz and muscovite or illite frequently along with biotite, chlorite, hematite, and pyrite

Accessory minerals: Apatite, graphite, kaolinite, magnetite, tourmaline, or zircon as well as feldspar

Classification

Heat, pressure, and chemical reactions may change either igneous or sedimentary rock into metamorphic rock, meaning “changed in form,” usually into a more compact and crystalline condition, and even metamorphic rocks may be further altered to higher ranks of metamorphism.

Rocks may become plastic under great pressure and high temperature and by earth movement. They may be folded into complex forms with a banded structure. Many constitutes minerals may be dissolved, transported, and reprecipitated by thermal waters. Heat and pressure may cause recrystallization.

In this way, new rocks are formed, differing widely from the igneous or sedimentary types, and usually much harder than either. Thus shale and related rocks may be altered into slate.

The shale from which slates originate were deposited previously as clay beds. These beds of shale at first horizontal, were tilted by subsequent earth movements, and the intense metamorphism that converted these into slates folded and contracted them. Slate, then, belongs to the metamorphic group of rocks and can be defined as a fine-grained rock derived from clays and shale and possessing a cleavage that permits it to be split into two sheets.

Chemical Composition of Slate

Slate is particularly composed of the minerals quartz and muscovite or illite, frequently along with biotite, chlorite, hematite, and pyrite and, less regularly apatite, graphite, kaolinite, magnetite, tourmaline, or zircon as well as feldspar. Occasionally, as within the pink slates of North Wales, ferrous discount spheres form around iron nuclei, leaving a mild green noticed texture. These spheres are once in a while deformed by a next carried out pressure discipline to ovoids, which appear as ellipses while viewed on a cleavage plane of the specimen.

Formation of the Rock

Shale is deposited in a sedimentary basin where finer particles are transported by wind or water. These deposited fine grains are then compacted and lithified. Tectonic environments for producing slates are when this basin is involved in a convergent plate boundaries. The shale and mudstone in the basin is compressed by horizontal forces with minor heating. These forces and heat modify the clay minerals. Foliation develops at right angles to the compressive forces of the convergent plate boundaries.

Where is it Located

In Europe, most slate is mined in Spain. It is also mined in the United Kingdom, and parts of France, Italy, and Portugal. Brazil is the second-biggest producer of slate. In the Americas, it’s also found in Newfoundland, Pennsylvania, New York, Vermont, Maine, and Virginia. China, Australia, and the Arctic also have large reserves of slate.

Characteristics and Properties of Rock

  • It is a fine-grained, metamorphic rock formed by compression of sedimentary shale, mudstone, or basalt.
  • Gray slate is common, but the rock occurs in a variety of colors, including brown, purple, green, and blue.
  • It consists mainly of silicates (silicon and oxygen), phyllosilicates (potassium and aluminum silicate), and aluminosilicates (aluminum silicate).
  • The term “slate” also refers to objects made from the rock, such as slate tablets or roofing tiles.
  • The phrases “clean slate” and “blank slate” refer to slate’s use in chalkboards.

Uses of Rock

It can be made into roofing slates, a type of roof shingle, or more specifically a type of roof tile.

A “slate boom” occurred in Europe from the 1870s until the first world war, allowed by the use of the steam engine in manufacturing slate tiles and improvements in road and waterway transportation systems.

It is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%, making the material waterproof.

Natural slate is used by building professionals as a result of its beauty and durability.

Its low water absorption makes it very resistant to frost damage and breakage due to freezing. Natural slate is also fire resistant and energy efficient.

Because it is a good electrical insulator and fireproof, it was used to construct early-20th-century electric switchboards and relay controls for large electric motors. Fine slate can also be used as a whetstone to hone knives.

Due to its thermal stability and chemical inertness, slate has been used for laboratory bench tops and for billiard table tops.

In areas where it is available, high-quality slate is used for tombstones and commemorative tablets. In some cases slate was used by the ancient Maya civilization to fashion stelae.

Slate was traditional material of choice for black Go stones in Japan. It is now considered to be a luxury.

Facts About Rock

  • Slate is mostly made of clay but the clay can change to mica under extreme degrees of pressure.
  • The color of slate is largely determined by the amount of iron it contains, but it is normally a shade of gray.
  • Slate normally forms in basins between convergent plate boundaries.
  • Often, slate is used to describe shale but the two are different in that shale is actually converted into slate.
  • Slate is used for different varieties of flooring and roofing.
  • School children used pieces of slate as a writing board to practice their math and writing during the 1800s.
  • Slate can easily be broken into neat, thin sheet because of its foliation.
  • The majority of mined slate is used for roofing because it does not absorb a lot of water and can withstand freezing air.
  • Slate is very expensive to make and install.
  • Chalk boards are made of slate and chalk is made of limestone, another type of rock.
  • Slate is used to make turkey calls which are devices that mimic the sound of different turkeys and used by hunters.
  • Slate has a wet-like appearance when exposed to the sun.
  • Slate is produced worldwide but the best slate is said to come from certain countries such as Brazil and the United Kingdom.
  • Slate can be found in various places such as on the sides of cliffs, underground, and in pits.
  • Slate normally is formed from a sedimentary rock.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.

Wikipedia contributors. (2019, February 24). Slate. In Wikipedia, The Free Encyclopedia. Retrieved 03:03, April 9, 2019, from https://en.wikipedia.org/w/index.php?title=Slate&oldid=884895818

Cite this article as: Geology Science. (2019). Slate. [online] Available at: http://geologyscience.com/rocks/metamorphic-rocks/slate/ [8th December 2019 ]
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