Ganister
In addition to underclays, ganisters also occur as seatearths. Like fireclays, they also found within Carboniferous and other sedimentary strata independent of coal beds. Thus, as in case of fireclays, not all ganisters are seatearths. Ganisters are indurated, fine-grained quartzose sandstones, which can be used in the manufacture of silica brick. It is cemented with secondary silica and has a characteristic splintery fracture.
As defined, ganisters can either be created by either the cementation of quartzose by surficial soil-forming processes to form silicrete or by diagenetic cementation within the subsurface. Detailed studies of ganisters, which occur either as seatearths or elsewhere within coal-bearing strata, have found them to be ancient paleosols, which are equivalent in both physical characteristics and origin to modern silica-cemented soils, called silcretes. The modern equivalent of ganisters have been observed in the process of being formed in the Okavango Delta of Botswana.
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