Figure 4- 1 Morphology of Natural Copper Aggregate
The physical properties of natural minerals are metallic color, metallic luster, strong reflection and opacity. No cleavage; Low hardness; Strong ductility. High density. Good electrical and thermal conductivity. Often dendritic, often forming twins.
In terms of mineral genesis, natural gold is often hydrothermal, while natural copper and natural silver are more common in the oxidation zone of sulfide deposits besides hydrothermal genesis, and are reduced by copper sulfate or silver sulfate solution formed by oxidation of sulfide minerals containing copper or silver by other sulfates or sulfides.
Natural copper family
Copper)
Equiaxial crystal system. Single crystals are rare, and usually exist in the form of irregular dendritic (Figure 4- 1), flaky or dense massive aggregates.
Copper red, often with actinide color on the surface; Striped copper red; Metallic luster; Opaque. The hardness is 2.5 ~ 3; No cleavage; The fracture is serrated; Strong ductility. The density is 8.95g/cm3 (pure copper). The melting point is 1083℃. It has good electrical and thermal conductivity.
Native copper is the reduction product of various geological processes. Natural copper of hydrothermal origin is often scattered; Natural copper, which is filled in the pores of basalt and produced together with minerals such as zeolite and prehnite, is related to volcanic hydrothermal process. Natural copper of sedimentary origin exists in some sedimentary rocks rich in organic matter. The most common is native copper formed in the lower part of the oxidation zone of copper-bearing sulfide deposits, which is oxidized by copper-bearing sulfide and reduced by other sulfates or sulfides, and often coexists with chalcopyrite, hematite, malachite and other minerals.
★ The main distinguishing feature is copper red, metallic luster, ductility and high density.
When accumulated in large quantities, it can be used as copper ore.
Gold) Au (natural gold)
Equiaxial crystal system. Single crystals are rare, usually in the form of dispersed granular, flaky and dendritic aggregates, and occasionally there are larger gold nuggets (commonly known as "gold nuggets").
Golden yellow, the stripes are the same color, and the color gradually turns pale yellow with the increase of Ag content in its composition; Metallic luster, opaque. The hardness is 2.5 ~ 3; No cleavage; Strong ductility, can be hammered into gold foil or drawn into gold wire. The density is 19.3g/cm3 (pure gold). The melting point is 1062℃. A good conductor of heat and electricity. Chemical stability, insoluble in acid, only soluble in aqua regia.
Natural gold is almost the only source of gold. It is mainly formed in gold-bearing quartz veins caused by high and medium-temperature hydrothermal fluids, or in altered rocks and medium-and low-temperature hydrothermal deposits related to volcanic hydrothermal processes. Natural gold is often enriched under exogenous conditions because of its high density and stable chemical properties, forming important placer gold deposits.
Many provinces and regions in China have natural gold producing areas, among which the primary deposit in Shandong Jiaodong Peninsula is the most famous, while placer gold deposits are most distributed in Jinsha River, Heilongjiang, Jilin and Shui Yuan Basin in Hunan.
★ The main distinguishing features are golden yellow and striped color, low hardness, strong ductility and high density, which are insoluble in general strong acids.
Gold is the currency in the international financial market. In addition, it is also used to make jewelry, prepare various alloys and make parts of cutting-edge technical equipment.