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Encyclopedia of Global Resources part 59 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. . | 528 Gold Global Resources placer deposits formed in this manner. Among the more famous nuggets found are a 93-kilogram nugget found in Hill End Australia and a 153-kilogram nugget found in Chile. The spectacular classic placer deposits found in the Klondike in the Yukon Canada and near Sacramento California explain the subsequent gold bonanzas and migration of prospectors then settlers into the American West. Secondary deposits have also yielded the abundant alluvial gold deposits found near Johannesburg. By far most gold is found in placers of sedimentary origin. In areas of recent erosion gold is usually found in small shapeless grains in small sheets or as flakes. When fine-grain gold is found in alluvial deposits panning for gold is performed to separate the precious metal from the sand. Formed in primary deposits crystals of elemental gold may occur as veins or as dendritic arborescent aggregates in association with quartz crystals. Dendritic aggregates look as though the metallic cr ystal developed with a fernlike growth on large colorful and translucent quartz cr ystals. Gold veins are often natural alloys of gold and silver rather than pure gold. These naturally occurring gold-silver alloys are known as electrum in which the silver content may range from 15 percent to 50 percent. Other natural alloys as of gold and palladium porpezite or gold and rhodium rhodite are less frequently found. Gold also occurs in telluride ores such as tetradymite nagyagite and sylvanite. These ores are primarily sulfide compounds of tellurium. In addition to tellurium Te and sulfur S atoms tetradymite contains gold and lead. Similarly sylvanite and nagyagite black tellurium contain gold and silver but in different arrangements and ratios. Elemental gold can be extracted from these minerals via chemical reactions. Gold is not an essential element for life although trace amounts are found in humans and some plants concentrate the element. Trace amounts in humans may arise from .
