tailieunhanh - Encyclopedia of Global Resources part 84

Encyclopedia of Global Resources part 84 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. . | 758 Minerals structure and physical properties of Global Resources topaz 9 corundum and 10 diamond. Minerals can scratch other minerals of the same or lesser hardness. The hardness of minerals can be tested using common materials including the fingernail a little over 2 copper about 3 a steel nail or pocket knife a little over 5 a piece of glass about and a steel file . Color Although color is a prominent feature of minerals it is not a reliable indicator for identifying minerals. The color of some minerals is the result of major elements in their chemical formula such as the blue color of azurite and the green color of malachite copper the pink color of rhodonite and rhodochrosite manganese and the yellow color of sulfur. Many minerals come in a variety of colors. Quartz is colorless and transparent when pure but it may also be white milky quartz pink rose quartz purple amethyst yellow citrine brown smoky quartz or other colors. Similarly feldspar and fluorite come in many hues. Color may be caused by impurities such as iron pink green or greenish yellow titanium pink or blue chromium red or green vanadium green and nickel yellow . Milky quartz is white because it contains tiny fluid inclusions. Coloration can be the result of defects in the crystal structure for example the purple of amethyst and fluorite and the brown of smoky quartz. Unusual colors may also be induced in minerals by exposing them to radiation which damages the cr ystal structure such as black quartz . Luster Luster refers to the shine or quality of reflectivity of light from the mineral s surface. Minerals can be divided into two luster groups metallic luster and nonmetallic luster. Metallic minerals include economically valuable metals such as gold silver and native copper and some metal sulfides such as pyrite FeS2 or iron sulfide and galena PbS or lead sulfide . Nonmetallic minerals include those with vitreous or glassy luster quartz earthy or dull luster kaolinite and other clays .