Ganister
Encyclopedia
A ganister is hard, fine-grained quartzose sandstone
, or orthoquartzite, used in the manufacture of silica brick typically used to line furnaces. Ganisters are cemented with secondary silica and typically have a characteristic splintery fracture.
Cornish miners originally coined this term for hard, chemically and physically inert silica-cemented quartzose sandstones, commonly, but not always found as seatearth
s within English Carboniferous
coal measures. This term is now used for similar quartzose sandstones found typically as seatearths in the Carboniferous coal measures of Nova Scotia
, the United States, and the Triassic coal-bearing strata of the Sydney Basin in Australia
.
Where a ganister underlies coal
as a seatearth, it typically is penetrated by numerous root traces. These root traces typically consist of carbonaceous material. Ganisters that contain an abundance of fossil roots, which appear as fine carbonaceous, pencil-like streaks or markings, are called “pencil ganisters”. In other cases, the root traces consist of fine, branching nodules, called “rhizoliths”, which formed around the roots before they decayed.
From detailed studies of ganisters, geologists have concluded that the typical ganister is the silicified surface horizons, i.e. E horizon, of a buried soil, called “paleosol”, developed in sandy sediments. These and other studies have found ganisters to contain abundant evidence of having once been the upper horizon of a soil
, which has developed in loamy or sandy sediments. The evidence includes some combination of carbonized roots and rootlets, rhizoliths, illuvial clay cutans, silcrete-like silica cements, and the leaching and alteration of the sandy sediments by weathering and plants. These studies argue that the destruction of easily weathered minerals, i.e. feldspar, within the surface horizon of a soil by soil-forming processes is what creates the quartz-rich nature of ganisters. The silica-cementation that creates a ganister typically results from dissolution of plant opal within a soil profile and its redeposition as silica cement within it. The formation of ganisters have been observed within modern soils, such as in the Okavango Delta of Botswana.
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, or orthoquartzite, used in the manufacture of silica brick typically used to line furnaces. Ganisters are cemented with secondary silica and typically have a characteristic splintery fracture.
Cornish miners originally coined this term for hard, chemically and physically inert silica-cemented quartzose sandstones, commonly, but not always found as seatearth
Seatearth
Seatearth is a British coal mining term, which is used in the geological literature. As noted by Jackson, a seatearth is the layer of sedimentary rock underlying a coal seam. Seatearths have also been called seat earth, "seat rock", or "seat stone" in the geologic literature. Depending on its...
s within English Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
coal measures. This term is now used for similar quartzose sandstones found typically as seatearths in the Carboniferous coal measures of Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
, the United States, and the Triassic coal-bearing strata of the Sydney Basin in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Where a ganister underlies coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
as a seatearth, it typically is penetrated by numerous root traces. These root traces typically consist of carbonaceous material. Ganisters that contain an abundance of fossil roots, which appear as fine carbonaceous, pencil-like streaks or markings, are called “pencil ganisters”. In other cases, the root traces consist of fine, branching nodules, called “rhizoliths”, which formed around the roots before they decayed.
From detailed studies of ganisters, geologists have concluded that the typical ganister is the silicified surface horizons, i.e. E horizon, of a buried soil, called “paleosol”, developed in sandy sediments. These and other studies have found ganisters to contain abundant evidence of having once been the upper horizon of a soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
, which has developed in loamy or sandy sediments. The evidence includes some combination of carbonized roots and rootlets, rhizoliths, illuvial clay cutans, silcrete-like silica cements, and the leaching and alteration of the sandy sediments by weathering and plants. These studies argue that the destruction of easily weathered minerals, i.e. feldspar, within the surface horizon of a soil by soil-forming processes is what creates the quartz-rich nature of ganisters. The silica-cementation that creates a ganister typically results from dissolution of plant opal within a soil profile and its redeposition as silica cement within it. The formation of ganisters have been observed within modern soils, such as in the Okavango Delta of Botswana.