A ganister (or sometimes gannister[1] ) is hard, fine-grained quartzose sandstone, or orthoquartzite,[2] used in the manufacture of silica brick typically used to line furnaces.
Cornish miners originally coined this term for hard, chemically and physically inert silica-cemented quartzose sandstones, commonly, but not always found as seatearths 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.
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.