Ganister

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 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.

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.