tailieunhanh - Encyclopedia of Global Resources part 5

Encyclopedia of Global Resources part 5 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 . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 10 Aggregates Global Resources their durability and ability to be polished to an attractive gloss finish. Examples include large building ornaments countertops and headstones for graves. Sand and gravel are found in areas with past or existing streamflow. In many cases the segregating aspects of streamflow have sized the sand and gravel so that further sizing is minimized. Crushed stone however is produced in mining operations and the operator has control over the size range of the finished product. For the most part these operations are at the surface and are known as quarries. Some stone is produced in underground mining operations with the high quality of the stone justifying the additional expense of this type of operation. Many quarries operating in a particularly desirable deposit of stone continue to pursue it by going underground. Preparations for Mining Before any significant expense is committed to locating and developing an aggregate production site a market study is performed to determine the amount and quality of materials needed within a certain radius of transportation. Experienced aggregate producers usually have a sixth sense about the need for and location of their products. After the marketing study has been completed a quarr y site is located by geological exploration techniques such as identification of surface outcrops of material or inference through regional studies of rock type. Even surface vegetation can indicate the type of material beneath the surface. Limestone terrains for example do not support acidic-soil vegetation because of their high pH values. The potential source of aggregate is identified and outlined more precisely through the digging of test pits for samples of the materials or by drilling test holes and analyzing the samples obtained. Again the inherent size of the naturally occurring materials and the estimated expense of preparing them to market specifications are critical points that help determine whether a site is to