Natural gold (Gold)

Au

[Chemical composition] There are often Ag-type homologous substitutions of Au in the composition, and both can form a complete class of the same image. In the ingredients

When the content of Ag<5% is called natural gold ; when Ag is 5%~15%, it is called silver natural gold; 15%~50% is called silver gold; 50%~85% is called gold and silver; 85%~95 % is called gold natural silver; >95% is called natural silver. In addition, natural gold chemical components also have a small amount of B, Pt, Cu, Pd, Te, Se, Ir and other elements.

[crystal structure] equiaxed crystal system; , with a copper structure (Fig. Z-1); a 0 = 0.408 nm; Z = 4.

[Form] It is usually an irregular granular aggregate (Fig. Z-2). In addition, dendritic, scaly, flaky, reticular, fibrous, and even larger aggregates are seen. Single crystals that are discernible to the naked eye are rare. Self-formed semi-automorphic crystals are often seen under the microscope. Common single shapes are: cube {100}, octahedron {111}, rhombohedron {110}, tetrahexahedron {210} and Four-horned three-octahedron {311}. Often (111) forms a twin crystal.

Figure Z-2 Natural gold produced in quartz veins

Chinese scholar Xue Junzhi (1993) believes that the form of natural gold has a metrical significance through a lot of research. Generally, the form of the deep part is relatively simple, and the form of the shallow part is complicated. The general trend is that the deep part is dominated by the octahedron {111}, the middle part is dominated by the rhombohedron {110}, the shallow part is the tetragonal octahedron {311}, the triangular three octahedron {223} or other The complex form is dominant.

[Physical properties] Both color and streak color are golden yellow, but gradually become shallower with the increase of Ag content in the composition. The higher the Ag content, the lighter the color, and the pale yellow to milky yellow to silver gold ore. When Cu is contained, the color becomes dark and dark yellow; the metallic luster increases with the increase of the content of Ag. No clerk. Hardness 2.5 to 3. The relative density is 19.3 (pure gold). It has strong ductility and can be hammered into gold foil or drawn into filaments. Melting point 1062 ° C. A good conductor for heat and electricity. It is chemically stable, insoluble in acid, and soluble in aqua regia. Does not change color after burning.

[genesis and production] Natural gold is mainly formed in various high and medium temperature hydrothermal action and metamorphism.

The main types of gold deposits in the world are: various hydrothermal vein type gold deposits, metamorphic conglomerate type gold deposits, quartz vein type gold deposits in ancient metamorphic rocks, disseminated gold deposits in sedimentary rocks and gold deposits in the sand gold type. 80 years ago it discovered the largest gold deposits in metamorphic conglomerate type, after the 1990s, the United States, Australia, Canada, South Africa and other countries have found a series of hydrothermal quartz veins with a variety of effects associated with feldspar quartz veins The super-large gold mine has broken the long-standing pattern of the world's main source of gold with metamorphic conglomerate-type gold deposits.

In recent years, the state has invested a large amount of money to find gold mines, but there has been no major breakthrough in gold-seeking work. At present, China has not found a world-class super-large gold mine. The main types of gold deposits that have been discovered in China are hydrothermal and weathering, and sand gold. The most famous gold mines are Shandong, Hunan, Henan, Heilongjiang, Jilin, Liaoning and Inner Mongolia.

[identification characteristics] golden yellow, strong metallic luster, large relative density, low hardness, strong ductility; chemical stability, fire does not change color. It differs from pyrite addition to hardness, streaks, chemical stability and relative density properties, which is more easy distinction easily crushed.

[Main use] Natural gold is almost the only source of Au. The gold mined in various gold deposits is basically natural gold. The amount of gold reserves is one of the indicators for measuring the economic strength of a country and is a worldwide “hard currency”. In addition to being used to manufacture currency and decorations, it is also widely used in industry because of its excellent stability, thermal conductivity, and ductility, which are often used as coatings for advanced vacuum tubes, computers, televisions, and tape recorders. Gold-coated integrated circuits, linings for nuclear reactors, gold-coated heat shields or thermal shields for jet engines and rocket engines, and wire-drawing wires for special precision electronic instruments.

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