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The following is a list of rock types recognized by geologists. There is no agreed number of specific types of rock. There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
Chalk is a highly porous and permeable rock, and rain falling onto chalk topography percolates directly into the ground, where the chalk layer acts as an aquifer. The groundwater flows through the chalk bedrock, re-emerging lower down the slope in springs. The chalk acts as a temporary reservoir by regulating the amount of water supplied to the ...
The concept of permeability is of importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, [4] and of groundwater in aquifers. [5]For a rock to be considered as an exploitable hydrocarbon reservoir without stimulation, its permeability must be greater than approximately 100 md (depending on the nature of the hydrocarbon – gas reservoirs with lower ...
An unconfined aquifer has no impermeable barrier immediately above it, such that the water level can rise in response to recharge. A confined aquifer has an overlying impermeable barrier that prevents the water level in the aquifer from rising any higher. An aquifer in the same geologic unit may be confined in one area and unconfined in another.
A rock formation is an isolated, scenic, or spectacular surface rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term rock formation can also refer to specific sedimentary strata or other rock unit in stratigraphic and petrologic studies.
An artesian well is a well that brings groundwater to the surface without pumping because it is under pressure within a body of rock or sediment known as an aquifer. [1] When trapped water in an aquifer is surrounded by layers of impermeable rock or clay, which apply positive pressure to the water, it is known as an artesian aquifer. [1]
A craton is an ancient part of the Earth's continental crust which has been more or less stable since Precambrian times. Cratons whose ancient rocks are widely exposed at the surface, often with relatively subdued relief, are known as shields.
Weald Clay or the Weald Clay Formation is a Lower Cretaceous sedimentary rock unit underlying areas of South East England, between the North and South Downs, in an area called the Weald Basin. It is the uppermost unit of the Wealden Group of rocks within the Weald Basin, and the upper portion of the unit is equivalent in age to the exposed ...