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Clay Coal seams are just one part of a geological sandwich. The beds below the coal seams are unstratified clays generally known as underclays. The chemical and physical properties of this clay vary. It can be highly refractory, i.e. resistant to heating in which case it is termed Fireclay. It is ideal for making firebricks and crucibles. Sometimes the underclay has a high silica content and can resemble a hard flinty rock in this case it is known as Ganister. Ganister is also a refractory material used to make firebricks. In the Halifax area both fireclay and ganister have been mined and quarried. A number of companies also quarried shale to make common bricks. |
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