In nature, minerals produced by intact single crystals or crystalline vinegar are relatively rare and are generally found in cracks in crystal caves. This is because the important condition for the complete development of mineral vigilance is the need for good free growth space, and the supersaturation of the solution is relatively low, which makes the crystallization speed of minerals slow. Under certain temperature and pressure conditions, the fluid and the surrounding rock of the cave wall constantly interact, thus generating various well-developed mineral clusters.
China has a vast territory, complex geological background, different natural environmental conditions and widely distributed mineral clusters. Briefly introduce the most common and important.
Crystal is a timely crystal with good crystallization, and its chemical composition is silicon oxide (SiO2). A hexagonal object with a cone head, which is composed of a hexagonal double cone and a hexagonal cylinder in the crystal state. Its colors are various: colorless transparent or milky translucent crystal, purple amethyst, smoky gray smoky gray crystal, brown tan crystal, yellow topaz, rose Barasuishou (hibiscus stone) and so on. Amethyst is one of the most popular gems. In addition to its elegant color, our ancestors also believed that amethyst can promote mutual understanding and bless peace and everything goes well. The international gemmological circle lists amethyst as the birthstone in February.
Most crystals are produced in the form of single crystal clusters, and sometimes they may be produced together with other mineral clusters (such as fluorite, barite, Cinnabar or specularite). The specularite produced with it is often a petal-shaped aggregate, which constitutes an "iron rose" with a very beautiful shape. Crystal clusters themselves often form chrysanthemum-like radial aggregates, which are deeply loved by people. Almost all provinces (cities and autonomous regions) in China produce crystals, but Jiangsu, Guizhou, Sichuan, Neijingu, Hainan and other provinces are abundant. Abroad, Brazil is famous for its abundant crystals, especially amethyst, and other producing areas include Madagascar, Japan and the United States.
Crystal deposits are mainly granite pegmatite type and medium-temperature hydrothermal filling type. The former mostly occurs in the inner and outer contact zone of granite, while the latter is distributed in siliceous rocks (such as quartzite, sandstone, siliceous shale and gneiss), limestone and dolomite, and occurs in vein and lenticular crystal caves.
Calcite Calcite is also a widely distributed common mineral crystal (cluster). Its chemical composition is calcium carbonate (CaCO3), which is mainly colorless or white, and sometimes it is light yellow, light red, purple, brown and black due to other elements. Colorless and transparent calcite crystals, called Iceland spar, are important optical materials. Calcite crystals are generally well developed and have various forms, such as columnar, rhombic, tabular and triangular bodies. The size of a single crystal can range from a few millimeters to dozens of centimeters. Therefore, calcite clusters are rich in shape and beautiful in shape. Sometimes, calcite clusters can coexist with metal sulfide crystals (such as pyrite and sphalerite), and their shapes are more beautiful. When I visited the Shuikoushan lead-zinc mine in Hunan Province, I saw a huge and spectacular crystal cave dominated by calcite clusters, which could accommodate dozens of people. In some places, rhombic calcite clusters and translucent brown sphalerite crystals can be seen, forming beautiful patterns. Calcite crystal clusters are mainly produced in hydrothermal vein deposits surrounded by carbonate rocks, such as Guizhou, Guangxi, Yunnan and other provinces. There are a large number of carbonate strata in these areas, and magmatic activities are not developed, so their formation temperature is generally slightly lower than that of crystals.
Fluorite Fluorite is a kind of calcium fluoride (CaF2). Mineral crystals are mostly translucent to transparent and show strong fluorescence under ultraviolet irradiation. Minerals often appear in various attractive colors, including red, green, blue, brown, yellow, orange and purple. Crystals are usually cubes, and two cubes often interpenetrate each other to form twins, followed by octahedron and rhombic dodecahedron. The size of a single crystal can range from a few millimeters to dozens of centimeters.
Most fluorite is formed in hydrothermal stage. According to the different surrounding rocks, it can be roughly divided into two types: one is produced in silicate rocks, such as granite, rhyolitic volcanic rocks, shale and sandstone, and the main biological minerals are calcite, barite and various metal sulfides, such as sphalerite, galena, chalcopyrite and pyrite. China is rich in fluorite resources, and crystal clusters are often well developed, which are produced in Zhejiang, Shandong, Liaoning, Guangdong, Yunnan, Hunan, Guizhou, Sichuan and other provinces.
Beryl This is an aluminosilicate mineral containing beryllium (Be3Al2Si6O 18). Crystals often form hexagonal columns and hexagonal cones, which have glass luster. Due to the differences between alkali metals and trace elements, they can present different colors, such as colorless, green, blue, rose, purple and so on. Emerald is the most precious member and gem of beryl family. Its bright green color is attributed to the presence of chromium and vanadium in minerals. Emerald green is pleasing to the eye and fascinates people of all ages. It has the reputation of "the king of green" and is especially loved by the eastern nations. Since ancient times, emeralds, together with diamonds, rubies and sapphires, have been listed as the four greatest gems in the world.
Beryl generally occurs in granite pegmatite formed by high temperature gas-liquid interaction, and often coexists with crystal aggregates such as muscovite and microcline. The size of beryl single crystal varies from a few centimeters to dozens of centimeters. Altai region in Xinjiang is the main producing area of beryl, and it is also produced in Gansu, Yunnan and other provinces. However, the geological environment of emeralds is special. For example, emeralds in North Carolina are produced in granite pegmatite caves in ultrabasic rocks (an ultramafic intrusive rock). There is a vein scheelite-emerald deposit with high temperature gas maturity in Yunnan, China, which occurs in the outer contact zone of beryllium-bearing mica granite and is surrounded by ancient metamorphic rocks with high chromium and vanadium.
Its chemical composition is alumina (AI2O3), and its hardness is 9, which is second only to diamond (the hardness of diamond is 10). Natural corundum generally contains trace element impurities, mainly chromium, titanium, manganese, vanadium and so on. So corundum has different colors, yellow gray, blue gray, red, blue, purple, green, brown and black. The crystal forms of corundum are mostly barrel-shaped, columnar or plate-shaped, and most of them are relatively complete, with glass luster to diamond luster.
Ruby refers to transparent to translucent corundum, which is bright red in color and contains chromium. It is a very precious gem. At present, high-quality rubies on the market are more precious than diamonds. Ruby is famous in Myanmar, Thailand, Sri Lanka, Brazil and Vietnam. It is mainly produced in white coarse-grained marble in the outer contact zone of intrusive rocks, showing disseminated porphyry. The necessary geological conditions for its formation are high temperature, rich aluminum, lack of silicon and chromium sources. Ruby deposits of similar origin have also been found in Tibet and Yunnan.
Sapphire refers to gem-grade corundum, which can be of any color and tone except red. Their colors are white, yellow, cyan, blue, purple, rose and so on, but blue is the most common. Blue color is caused by titanium and iron existing in corundum crystals. Sapphire is mainly produced in Brazil, Myanmar, Thailand and Australia. However, its geological conditions are different from that of ruby, and it is mainly produced in alkaline basalt. There is also a sapphire deposit in Shandong, China, but the color of sapphire crystal is too dark. Another kind of sapphire occurs in skarn in the internal contact zone between alkaline intrusive rocks and magnesium-rich carbonate rocks.
Antimony belongs to antimony sulfide (Sb2Ssss3), which is lead-gray and has metallic luster. The single crystal is long columnar or needle-shaped, and the cylindrical surface has obvious longitudinal stripes. Crystal aggregates are usually radial or beam-shaped. The size of single crystals ranges from a few centimeters to dozens of centimeters. Antimony is the most widely distributed antimonide, which is found in low-temperature hydrothermal filling deposits. Xikuangshan, Hunan, China is the largest and most famous stibnite producing area in the world, and there are also many stibnite deposits in Guizhou, Guangxi, Shaanxi and other provinces. In addition to some common and precious mineral clusters listed above, there are many beautiful and common mineral clusters in nature, such as garnet, pyrite, cassiterite, cinnabar, kyanite, malachite, realgar, orpiment, tourmaline, gypsum, amphibole, epidote, andalusite, celestite and apophyllite. Limited by space, I can't list them all here.
Mineral crystal cluster is an important ornamental stone. Western countries such as Europe and America highly admire and love mineral clusters, and the collection results are remarkable. With the rapid development of China's economy and the continuous improvement of people's material life and cultural level, the exploitation and development of ornamental stones, especially mineral crystal clusters, has also risen rapidly and become one of the symbols of a country's culture and civilization.
Because mineral crystals are naturally formed, not man-made, and are valuable non-renewable resources. They are not only regional, rare, peculiar, artistic, scientific and commercial, but also have ornamental, pondering, display, collection and scientific research value. They are favored by more and more people with their peculiar crystal forms, various shapes, colorful colors and beautiful and precious textures, which are pleasing to the eye and memorable. Throughout China, especially in big cities, there is an upsurge in the collection, exhibition and management of ornamental stones, especially mineral crystal clusters. For example, in Beijing, Guilin and other places, there are at least dozens of shops selling strange stones, ornamental stones and mineral crystal strings. However, at present, the investigation of new genesis of mineral crystal clusters, the study of geological environment and formation mechanism, artistic processing, rational development and utilization and resource protection are far from enough, and they often only pursue temporary commercial value, ignoring resource protection and its artistic and scientific value. This is a problem that should be paid attention to in the future.