Cement Stone

Cement Stone, a limestone, earthy and ferruginous, and containing an admixture of clay and often sand. When burnt, so as to convert the carbonate of lime in it into quicklime, this rock yields a hydraulic cement. A tolerable hydraulic limestone contains 10 per cent. of insoluble matter in addition to carbonate of lime; but one with 20 to 30 per cent. is better. The lias is our chief source of cement-stone; but the calciferous sandstone series (q.v.) of Scotland, the septaria (q.v.) from the London and other clays, and the ironstone known as "curl" in Coalbrookdale, are also of importance. More of our hydraulic cements are, however, manufactured by the admixture of ingredients than by calcination of natural limestones.