new, unstrained, small quartz grains, producing a mortar texture that can be identified in thin sections under a polarizing microscope. With increasing grade of metamorphism, further recrystallization produces foam texture, characterized by polygonal grains meeting at triple junctions, and then porphyroblastic texture, characterized by coarse, irregular grains, including some larger grains (porphyroblasts.) Uses Sandstone has been used since prehistoric times for construction, decorative art works and tools. It has been widely employed around the world in constructing temples, churches, homes and other buildings, and in civil engineering. Although its resistance to weathering varies, sandstone is easy to work. That makes it a common building and paving material, including in asphalt concrete. However, some types that have been used in the past, such as the Collyhurst sandstone used in North West England, have had poor long-term weather resistance, necessitating repair and replacement in older buildings. Because of the hardness of individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone. A type of pure quartz sandstone, orthoquartzite, with more of 90–95 percent of quartz, has been proposed for nomination to the Global Heritage Stone Resource. In some regions of Argentina, the orthoquartzite-stoned facade is one of the main features of the Mar del Plata style bungalows. See also Notes Bibliography Folk, R.L., 1965, Petrology of sedimentary rocks PDF version. Austin: Hemphill's Bookstore. 2nd ed. 1981, . Pettijohn F. J., P.E. Potter and R. Siever, 1987, Sand and sandstone, 2nd ed. Springer-Verlag. . Scholle, P.A., 1978, A Color illustrated guide to constituents, textures, cements, and porosities of sandstones and associated rocks, American Association of Petroleum Geologists Memoir no. 28. . Scholle, P.A., and D. Spearing, 1982, Sandstone depositional environments: clastic terrigenous sediments , American Association of Petroleum Geologists Memoir no. 31. . USGS Minerals Yearbook: Stone, Dimension, Thomas P. Dolley, U.S. Dept. of the Interior, 2005 (format: PDF). Further reading Webb, Jonathan. Sandstone shapes 'forged by gravity' (July 2014), BBC News Industrial minerals Building stone