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Encyclopedia of Global Resources part 4 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the U.S. Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | A Abrasives Category Mineral and other nonliving resources Abrasives comprise a large number of both naturally occurring minerals and rocks and manufactured products. In many cases these manufactured products have largely replaced their natural counterparts. Some such as diamond are rare others including sand and sandstone are found abundantly in nature. All find uses in the home or in industry because of their characteristic hardness. Background Because the abrasives category encompasses a great variety of materials their worldwide distributions are highly varied. Some such as garnet and emery are obtained from only a few localities. Others such as sand and sandstone are found on all continents in all geologic settings and in rocks representing all geologic ages. Use of all the abrasives reflects in some manner the characteristics of hardness. That property is utilized in cutting and drilling tools surface polishing materials and blasting media. The largest user of abrasives is the automobile industry. Abrasives both natural and synthetic are used to perform one of four basic functions the removal of foreign substances from surfaces dressing cutting drilling and comminution or pulverizing of materials. Most abrasives lie toward the upper end of the Mohs hardness scale. With respect to one another however they can be categorized as hard moderate or siliceous or soft. Hard Abrasives The hard abrasives are diamond corundum emer y and garnet. Diamond the hardest naturally occurring substance 10 on the Mohs scale is normally used in three size categories stone bort and powder. Only a small fraction of the diamond stones produced by mining are of gem quality. All others as well as those produced synthetically together referred to as industrial diamonds are used in various industrial applications including diamond saws rock-drilling bits and other abrasive tools. Bort consists of frag ments and small flawed stones. Most bort as well as synthetic diamond is crushed to .
