The term stone is applied to rock that is cut, shaped, broken, crushed, and otherwise physically modified for commercial use. The two main divisions are dimension stone and crushed stone. Other descriptive terms may be used, for example, building stone, roofing stone, or precious stone. See also Gem; Rock.
The term dimension stone is applied to blocks that are cut and milled to specified sizes, shapes, and surface finishes. The principal uses are for building and ornamental applications. Granites, limestones, sandstones, and marbles are widely used; basalts, diabases, and other dark igneous rocks are used less extensively. Soapstone is used to some extent. Rock suitable for use as dimension stone must be obtainable in large, sound blocks, free from incipient cracks, seams, and blemishes, and must be without mineral grains that might cause stains as a result of weathering. It must have an attractive color, and generally a uniform texture.
Slate differs from other dimension stone because it can be split into thin sheets of any desired thickness. Commercial slate must be uniform in quality and texture and reasonably free from knots, streaks, or other imperfections, and have good splitting properties. Roofing slates are important products of most slate quarries. However, the roofing-slate industry has declined considerably because of competition from other types of roofing. Slate is also used for milled products such as blackboards, electrical panels, window and door sills and caps, baseboards, stair treads, and floor tile. See also Slate.
Nearly all the principal types of stone—granite, diabase, basalt, limestone, dolomite, sandstone, and marble—may be used as sources of commercial crushed stone; limestone is by far the most important. Crushed stone is made from sound, hard stone, free from surface alteration by weathering. Stone that breaks in chunky, more or less cubical fragments is preferred. Commercial stone should be free from certain deleterious impurities, such as opalescent quartz, and free from clay or silt. Crushed stone is used principally as concrete aggregate, as road stone, or as railway ballast. Other uses for limestone are as a fluxing material to remove impurities from ores smelted in metallurgical furnaces, in the manufacture of alkali chemicals, calcium carbide, glass, paper, paint, and sugar, and for filter beds and for making mineral wool.
