See the full definition for shale in the English Language Learners Dictionary. Nglish: Translation of shale for Spanish Speakers. Britannica English: Translation of shale for Arabic Speakers. Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free! Log in Sign Up. Save Word. Definition of shale. Keep scrolling for more. Examples of shale in a Sentence Recent Examples on the Web The path was simply a horizontal shelf of the shale and limestone bedrock, maybe eight feet wide.
First Known Use of shale , in the meaning defined above. History and Etymology for shale probably from obsolete or dialect shale scale, shell, from Middle English, from Old English scealu — more at shell. Learn More About shale. Shale forms via compaction from particles in slow or quiet water, such as river deltas, lakes, swamps, or the ocean floor.
Heavier particles sink and form sandstone and limestone , while clay and fine silt remain suspended in water. Over time, compressed sandstone and limestone become shale. Shale typically occurs in a broadsheet, several meters thick. Depending on the geography, lenticular formations may also form. Sometimes animal tracks , fossils , or even imprints of raindrops are preserved in shale layers. The clay clasts or particles in shale are less than 0. The clay comes from decomposition of feldspar.
Shale consists of at least 30 percent clay, with varying amounts of quartz , feldspar, carbonates, iron oxides, and organic matter. Oil shale or bituminous also contains kerogen , a mixture of hydrocarbons from deceased plants and animals.
Shale is classified based on its mineral content. There is siliceous shale silica , calcareous shale calcite or dolomite , limonitic or hematitic shale iron minerals , carbonaceous or bituminous shale carbon compounds , and phospatic shale phosphate.
The color of shale depends on its composition. Shale with a higher organic carbon content tends to be darker in color and may be black or gray. The presence of ferric iron compounds yields red, brown, or purple shale. Ferrous iron yields black, blue, and green shale. Shale containing a lot of calcite tends to be pale gray or yellow. The grain size and composition of minerals in shale determine its permeability, hardness, and plasticity.
In general, shale is fissile and readily splits into layers parallel to the bedding plane, which is the plane of clay flake deposition. Shale is laminated , meaning the rock consists of many thin layers that are bound together. Shale has many commercial uses. It is a source material in the ceramics industry to make brick, tile, and pottery. Shale used to make pottery and building materials requires little processing besides crushing and mixing with water.
Crushing shale and heating it with limestone makes cement for the construction industry. Heat drives off water and breaks limestone into calcium oxide and carbon dioxide. Carbon dioxide is lost as a gas, leaving calcium oxide and clay, which harden when mixed with water and dried. In the case of shale with fossil deposits, the deposits form as a result of biological material which became trapped in the shale while it was being deposited and subjected to pressure.
In some cases, parts of the organism may be represented in mineralized form, while in others, the rock holds only the impression of a organism which decayed after the rock started to harden. In manufacturing, shale is used as a filler material for concrete and brick. People sometimes confuse this rock with slate, a much harder rock which can be used for a wide variety of purposes including roofing, tiling, blackboards, and so forth. In the case of slate, the rock is subjected to metamorphic processes which change the structure and properties of the rock, making it harder and more durable.
Although slate also bears distinctive layers and tendency to split along these layers when stressed, it is much harder than shale. Oil shale is not necessarily a shale, although it sometimes is, and it shares many of the traits associated with true shales.
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