Đang chuẩn bị liên kết để tải về tài liệu:
Encyclopedia of Global Resources part 100

Encyclopedia of Global Resources part 100 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. . | 918 Peru Global Resources perlite s distinctive fracture pattern are often called perlite if they contain enough water to expand in a similar fashion. Description Distribution and Forms Perlite is a form of natural glass. Natural glasses form when molten lava from volcanoes is cooled rapidly. The lava hardens too quickly to allow crystals to grow resulting in a substance with a glassy rather than a stony texture. Perlite is distinguished from other forms of natural glass in that it contains many tiny curved fractures structured like the layers of an onion. These fractures may be microscopic or may be visible to the naked eye. Because of these fractures perlite breaks apart into small round pearl-like particles. Perlite has a waxy or pearly luster and may be gray green brown blue or red. The term perlite is also more loosely used to mean any natural glass that expands into a light frothy material when heated. Most of the world s perlite is found in the western half of the United States. New Mexico supplies about three-quarters of the nation s perlite. Because underground deposits of natural glass slowly crystallize into stony substances over time perlite is almost always found at or near the Earth s surface. Greece Hungary Japan Mexico and Turkey are also major producers of perlite. History Though perlite has been known as a volcanic rock for more than two thousand years it was not used industrially until the twentieth century. By the 1970 s it was a common product used in the horticultural industry. Obtaining Perlite Because perlite is found near the surface it is mined using the open-pit method. It is then crushed to the desired particle size and transported to a processing center where it is heated to expand it. Uses of Perlite The expanded perlite is used as an aggregate that is it is mixed with other substances such as gypsum to form plaster or cement to form concrete. Although perlite is not as strong or inexpensive as other aggregates such as sand or gravel .