Where is shale formed

The sand or gravel particles in sandstone and conglomerate are held together by a mineral cement. Coal, which consists entirely of compressed plant remains, is a major source of fuel. Most sedimentary rock starts forming when grains of clay, silt, or sand settle in river valleys or on the bottoms of lakes and oceans.

Year after year, these minerals collect and form broad, flat layers called beds or strata. The layers, which differ from one another in composition or texture, distinguish sedimentary from most igneous and metamorphic rock.

After thousands of years, the beds of fine silt and clay are squeezed into compact rock layers by the weight of other layers above them. Water that trickles slowly through layers of coarse sand and gravel, deposits mineral cement around these particles, cementing the layers together to form rock. Where the earth's crust is deformed or eroded, large areas of buried sedimentary rock may be exposed. Most fossils are found in sedimentary rock. The fossils formed when sediments covered dead plants and animals.

As the sediments changed to rock, either the remains or the outlines of the plants and animals were preserved. Some limestone is made entirely of fossil shells. Shales that are subject to heat and pressure alter into a hard, fissile, metamorphic rock known as slate , which is often used in building construction. Resources "shale". Chambers Dictionary of Science and Technology. Chambers Harrap Publishers Ltd. Shale is a sedimentary rock. Shale starts with bits of rock that erode off of larger rocks from contact with moving water and the weather.

Very fine particles of feldspar, quartz, mica, pyrite and other minerals settle to the bottom of still bodies of water, such as swamplands, deep parts of the ocean and deep, still lakes. The fine rock particles mix with decaying organic matter into a mud. Because weathering is a continual process, new layers are always building up.

The top layers press on the bottom layers with more and more pressure. 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.

The petroleum industry uses fracking to extract oil and natural gas from oil shale.