Exfoliation is a form of rock weathering, also referred to as onion skin weathering. It is characterized by a layer by layer erosion of the outer surface of the rock caused by chemical changes to the composition of the minerals, by differences in temperature between the outer surface and the interior of the rock, or by the expansion and separation of the outer surfaces due to moisture absorption.
Exfoiliation is sometimes known as 'Onion-skin weathering', because curved sheets peel off from rocks affected by it. This occurs in arid, hot desert environments, where there is a marked difference in temperature during the day and night (hot during the day, cold during the night). Because of this different minerals expand and contract by different amouts during heating and cooling, causing the rocks to disintergrate and peel, almost like that of shale with its foliated surface.
Exfoliation occurs because of differing rates of expansion and contraction on the rock surface due to temperature. Exfoliation can also occur due to chemical weathering of the outer surface of a rock body.
Mechanical exfoliation is the weathering of a rock structure by freeze/thaw cycles or temperature differentials between the rock surface and interior. The exfoliation is the breaking off of the outer layer from the intact interior, akin to the removal of an onion's layers being peeled from the onion. Some rock exfoliation occurs from chemical weathering, thus the distinction from mechanical exfoliation.
Exfoliation or 'onion skin' weathering occurs mainly in granitic rocks from temperature differences in the surface and subsurface due to heat, cold, and sunlight. The temperature differences can cause minute cracking which is further attacked by mechanical and chemical weathering, and the outer skin in shed, giving the rock body a rounded look.
exfoliation
Exfoliation
In some case chemical weathering can cause this (where new crystals form from old ones but where the volume of the new crystals is not the same as the original). In other cases the weathering process is temperature driven by water entering the porous layer of a weathering rock and freezing. This can split the rock parallel to the surface, giving it exfoliation layers. Some texts also imply that exfoliation domes are produced by by removal of vertical pressure relieving paleo stresses in the rock, this however would not be a weathering process.
The formation of an exfoliation dome begins with sheeting, when large masses of igneous rock, particularly, granite, are exposed by erosion, concentric slabs begin to break loose, this process occurs in part because of the great reduction in pressure when the overlying rock is eroded away, a process called unloading, and accompanying this unloading, the outer layers expand more than the rock below and thus separate from the rock body. Continued weathering eventually causes the slabs to separate and spall off, creating exfoliation domes.
Exfoliation of bodies of granite rock can occur from chemical weathering of the surface, differences in temperature, salt crystallization, and release of pressure.
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Exfoliation is the natural process of the loss of primary ("baby") teeth.
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exfoliation that is the process
exfoliation
Exfoliation
exfoliation
Exfoliation refers to the process of removing dead skin cells from the surface of the skin. It helps to improve the skin's appearance, texture, and overall health.
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Exfoliation
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The weathering process involved in the formation of tors is exfoliation (onion skin weathering). Exfoliation can be mechanical or chemical. Mechanically, exfoliation may be a result of the different expansion rates between exterior and interior layers. Chemically, the exterior of the rock can be chemically altered to minerals of higher volume, causing it to slough off from the rock to which it was formerly attached.