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A concretion is a hard, compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. [1] Concretions are often ovoid or spherical in shape, although irregular shapes also occur.
Calcite cement in an ooid-rich limestone; Carmel Formation, Jurassic of Utah. Minerals bond grains of sediment together by growing around them. This process is called cementation and is a part of the rock cycle. Cementation involves ions carried in groundwater chemically precipitating to form new crystalline material between sedimentary grains ...
The particulate matter then undergoes compaction and cementation at moderate temperatures and pressures . [ 5 ] : 265–280 [ 15 ] : 147–154 Before being deposited, sediments are formed by weathering of earlier rocks by erosion in a source area and then transported to the place of deposition by water , wind , ice , mass movement or glaciers ...
In sedimentology, compaction is the process by which a sediment progressively loses its porosity due to the effects of pressure from loading. This forms part of the process of lithification . When a layer of sediment is originally deposited, it contains an open framework of particles with the pore space being usually filled with water.
For example, in lithic sandstones, cementation is less extensive because pore space between framework grains is filled with a muddy matrix that leaves little space for precipitation to occur. This is often the case for mudrocks as well. As a result of compaction, the clayey sediments comprising mudrocks are relatively impermeable.
Soil structure affects aeration, water movement, conduction of heat, plant root growth and resistance to erosion. [26] Water, in turn, has a strong effect on soil structure, directly via the dissolution and precipitation of minerals, the mechanical destruction of aggregates [27] and indirectly by promoting plant, animal and microbial growth.
Portland cement is the most common type of cement and is a general purpose cement. The product is made with a combination of calcium, silicon, aluminum, iron, and other ingredients.
Cementation of copper is a common example. Copper ions in solution, often from an ore leaching process, are precipitated out of solution in the presence of solid iron . The iron oxidizes, and the copper ions are reduced through the transfer of electrons.