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.
Green shales are occasionally found. This should not be surprising because some of the clay minerals and micas that make up much of the volume of these rocks are typically a greenish color. Natural gas shale well: In less than ten years, shale has skyrocketed to prominence in the energy sector.
New drilling and well development methods such as hydraulic fracturing and horizontal drilling can tap the oil and natural gas trapped within the tight matrix of organic shales. Hydraulic properties are characteristics of a rock such as permeability and porosity that reflect its ability to hold and transmit fluids such as water, oil, or natural gas.
Shale has a very small particle size, so the interstitial spaces are very small. In fact they are so small that oil, natural gas, and water have difficulty moving through the rock. Shale can therefore serve as a cap rock for oil and natural gas traps, and it also is an aquiclude that blocks or limits the flow of groundwater. Although the interstitial spaces in a shale are very small, they can take up a significant volume of the rock.
This allows the shale to hold significant amounts of water, gas, or oil but not be able to effectively transmit them because of the low permeability. The oil and gas industry overcomes these limitations of shale by using horizontal drilling and hydraulic fracturing to create artificial porosity and permeability within the rock. Some of the clay minerals that occur in shale have the ability to absorb or adsorb large amounts of water, natural gas, ions, or other substances.
This property of shale can enable it to selectively and tenaciously hold or freely release fluids or ions. Expansive soils map: The United States Geological Survey has prepared a generalized expansive soils map for the lower 48 states.
Shales and the soils derived from them are some of the most troublesome materials to build upon. They are subject to changes in volume and competence that generally make them unreliable construction substrates. The clay minerals in some shale-derived soils have the ability to absorb and release large amounts of water. This change in moisture content is usually accompanied by a change in volume which can be as much as several percent. These materials are called " expansive soils.
Buildings, roads, utility lines, or other structures placed upon or within these materials can be weakened or damaged by the forces and motion of volume change. Expansive soils are one of the most common causes of foundation damage to buildings in the United States. Shale delta: A delta is a sediment deposit that forms when a stream enters a standing body of water.
The water velocity of the stream suddenly decreases and the sediments being carried settle to the bottom. Deltas are where the largest volume of Earth's mud is deposited.
The image above is a satellite view of the Mississippi delta, showing its distributary channels and interdistributary deposits. The bright blue water surrounding the delta is laden with sediment. Shale is the rock most often associated with landslides. Weathering transforms the shale into a clay-rich soil which normally has a very low shear strength - especially when wet. When these low-strength materials are wet and on a steep hillside, they can slowly or rapidly move down slope.
Overloading or excavation by humans will often trigger failure. Shale on Mars: Shale is also a very common rock on Mars. This photo was taken by the mast camera of the Mars Curiosity Rover. It shows thinly bedded fissile shales outcropping in the Gale Crater. Curiosity drilled holes into the rocks of Gale Crater and identified clay minerals in the cuttings. NASA image. An accumulation of mud begins with the chemical weathering of rocks. This weathering breaks the rocks down into clay minerals and other small particles which often become part of the local soil.
A rainstorm might wash tiny particles of soil from the land and into streams, giving the streams a "muddy" appearance. When the stream slows down or enters a standing body of water such as a lake, swamp, or ocean, the mud particles settle to the bottom. If undisturbed and buried, this accumulation of mud might be transformed into a sedimentary rock known as "mudstone. The shale-forming process is not confined to Earth.
The Mars rovers have found lots of outcrops on Mars with sedimentary rock units that look just like the shales found on Earth see photo. Home » Rocks » Sedimentary Rocks » Shale Shale Shale is the most abundant sedimentary rock and is in sedimentary basins worldwide. Article by: Hobart M. Landslide: Shale is a landslide-prone rock. The maturity of shales degree of diagenesis is also a factor that influences brittleness and fracturability, since crystal growth processes, particularly of clay minerals result in coarsening of particle size and resultant changes in texture.
Hillier, S. Clays and Minerals. Home » Materials. Shaw D. The mineralogical composition of shales. The image below shows weathering of sandstone and shale. The steep cliffs are made up of weathering-resistant sandstone, while the slope at the base of the cliff is composed of rock units containing a larger abundance of shale.
Impact on Soils: Rapid disintegration generally leads to deep soils, high in clay-size particles, so slow permeability for water. How it Forms: Shale forms by deposition of sediment in low-current environments, such as lakes or along ocean shores in deep water not affected by waves.
Distinguishing Features: Relatively soft, can easily be scratched with a nail or pocket knife, reacts to hydrochloric acid fizzes , often contains fossils.
Weathering Behavior: Strongly affected by chemical weathering, leading to rounded edges see image below. Impact on Soils: Abundance of calcite makes for alkaline soils, which do not acidify rapidly. How it Forms: In shallow oceans or lakes, by deposition of animal shells or by precipitation from solution. Sandstone Properties. Type: Sedimentary Distinguishing Features: Made up of relatively coarse particles, which can often be seen without a hand lens; feels gritty, like sandpaper; sedimentary structures can be seen, such as layering or fossils.
Main Minerals: quartz, some 'dirty' sandstones contain feldspars, muscovite Weathering Behavior: Can erode easily depending on the mineral composition of the cement which holds single grains together; affected by chemical and physical weathering; individual grains often very resistant to weathering i. How it Forms: Deposition of sediment on beaches, sand dunes, stream valleys. Shale Properties.
Type: Sedimentary Distinguishing Features: Very fine grained, composed of clay-sized minerals, often breaks into platy fragments, some contain fossils.
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