Shale is used in making bricks. Limestone, another common sedimentary rock, is made chiefly of the mineral calcite. Limestone is used for building, for making chalk, and for various other purposes. Cement is made of limestone with a little shale mixed in. Sandstone, made of sand, and conglomerate, composed of sand or gravel particles, are also commonly used for building.
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. Black shales are the shales that contain organic matter and can break down to form natural gas or oil.
They are all grey or black in colour. Specifically, lithified mud becomes stone and shale is thus known as "mudstone". Black, organic shales are the source rock for oil and gas deposits, obtaining their colour from carbon particles.
Oil and natural gas can migrate out of the shale, moving upwards where they are trapped within the pores of some other rock—such as sandstone. These deposits are known as conventional reservoirs since the fluid flows easily through the pores of the rock. Although drilling to extract oil and natural gas is possible, a large amount is still trapped inside the pore spaces of the shale.
Cement is used to make concrete and many other products for the construction industry. Oil shale: A rock that contains a significant amount of organic material in the form of solid kerogen. This specimen is approximately four inches ten centimeters across. Oil shale is a rock that contains significant amounts of organic material in the form of kerogen.
This is usually much less efficient than drilling rocks that will yield oil or gas directly into a well. Extracting the hydrocarbons from oil shale produces emissions and waste products that cause significant environmental concerns.
This is one reason why the world's extensive oil shale deposits have not been aggressively utilized. Shale core samples: When shale is drilled for oil, natural gas, or mineral resource evaluation, a core is often recovered from the well. The rock in the core can then be tested to learn about its potential and how the resource might be best developed. Shale is a rock composed mainly of clay-size mineral grains. These tiny grains are usually clay minerals such as illite, kaolinite, and smectite.
Shale usually contains other clay-size mineral particles such as quartz , chert , and feldspar. Other constituents might include organic particles, carbonate minerals, iron oxide minerals, sulfide minerals, and heavy mineral grains.
These "other constituents" in the rock are often determined by the shale's environment of deposition, and they often determine the color of the rock. Black shale: Organic-rich black shale. Natural gas and oil are sometimes trapped in the tiny pore spaces of this type of shale.
Like most rocks, the color of shale is often determined by the presence of specific materials in minor amounts. Just a few percent of organic materials or iron can significantly alter the color of a rock.
Shale gas plays: Since the late s, dozens of previously unproductive black organic shales have been successfully developed into valuable gas fields. See the article: " What is Shale Gas? A black color in sedimentary rocks almost always indicates the presence of organic materials. Just one or two percent organic materials can impart a dark gray or black color to the rock.
In addition, this black color almost always implies that the shale formed from sediment deposited in an oxygen-deficient environment. Any oxygen that entered the environment quickly reacted with the decaying organic debris. If a large amount of oxygen was present, the organic debris would all have decayed. An oxygen-poor environment also provides the proper conditions for the formation of sulfide minerals such as pyrite , another important mineral found in most black shales.
The presence of organic debris in black shales makes them the candidates for oil and gas generation. If the organic material is preserved and properly heated after burial, oil and natural gas might be produced. The Barnett Shale, Marcellus Shale , Haynesville Shale , Fayetteville Shale , and other gas-producing rocks are all dark gray or black shales that yield natural gas. Gray shales sometimes contain a small amount of organic matter.
However, gray shales can also be rocks that contain calcareous materials or simply clay minerals that result in a gray color. Utica and Marcellus Shale: Two black organic shales in the Appalachian Basin are thought to contain enough natural gas to supply the United States for several years. These are the Marcellus Shale and Utica Shale. Shales that are deposited in oxygen-rich environments often contain tiny particles of iron oxide or iron hydroxide minerals such as hematite , goethite, or limonite.
Just a few percent of these minerals distributed through the rock can produce the red, brown, or yellow colors exhibited by many types of shale. The presence of hematite can produce a red shale.
The presence of limonite or goethite can produce a yellow or brown 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.
Fracking involves injection of liquid at high pressure into the rock to force out the organic molecules. High temperatures and special solvents extract the hydrocarbons, leading to waste products that raise concerns about environmental impact. Up to the midth century, the term " slate " often referred to shale, slate, and schist. Underground coal miners may still refer to shale as slate, per tradition. These sedimentary rocks have the same chemical composition and may occur together.
The initial sedimentation of particles forms sandstone and mudstone. Shale forms when the mudstone becomes laminated and fissile. If shale is subjected to heat and pressure, it can metamorphose into slate.
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