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Spheroidal or woolsack weathering in granite on Haytor, Dartmoor, England Spheroidal weathering in granite, Estaca de Bares, A Coruña, Galicia, Spain Woolsack weathering in sandstone at the Externsteine rocks, Teutoburg Forest, Germany Corestones near Musina, South Africa that were created by spherodial weathering and exposed by the removal of surrounding saprolite by erosion.
A weathering rind represents the alteration of the outer portion of a rock by exposure to air or near surface groundwater over a period of time. Typically, a weathering rind may be enriched with either iron or manganese (or both), and silica, and oxidized to a yellowish red to reddish color.
The weathering of rocks by leaching and oxidising conditions results in the formation of clay-like [22] minerals such as goethite, lepidocrocite, and hematite. [22] Some of them can hold rare earth minerals as well as iron, nickel and the alumina for which it is often mined. [23] [24] [24] Laterite results from the weathering of basalt.
Weathering is relatively slow, with basalt becoming less dense, at a rate of about 15% per 100 million years. The basalt becomes hydrated, and is enriched in total and ferric iron, magnesium, and sodium at the expense of silica, titanium, aluminum, ferrous iron, and calcium. [52]
It is quite common for spheroidal weathering, a form of chemical weathering, to occur as groundwater circulates through orthogonal joint sets in the near-surface. [10] This process results in the alteration and disintegration of bedrock adjacent to the joints.
Watson Lake in the Granite Dells The Peavine Trail Dells Granite showing spheroidal weathering.. The Granite Dells is a geological feature north of Prescott, Arizona.The Dells consist of exposed bedrock and large boulders of granite that have eroded into an unusual lumpy, rippled appearance.
The concretions were created by the precipitation of iron, which was dissolved in groundwater. The iron was originally present as a thin film of iron oxide surrounding sand grains in the Navajo Sandstone. Groundwater containing methane or petroleum from underlying rock beds reacted with the iron oxide, converting it to soluble reduced iron ...
The Lower Cambrian Eriboll Group comprises a basal quartzite, locally with a basal conglomerate, followed by the distinctive Pipe Rock Member, a quartz arenite with white weathering skolithos trace fossils. The Pipe Rock is overlain by the Salterella Grit, a coarse sandstone, and the Fucoid Beds, a sequence of calcareous sandstone and siltstone.