Uncover the mysterious veil of "South Red agate"

Uncover the mysterious veil of "South Red agate"

The origin of "Nanhong"

The name "Nanhong" sounds like it has nothing to do with jewelry, and I don't know what it is. In fact, "Nanhong" is the abbreviation of "Nanhong". What is "Nanhong"? yes, it is one of agate. According to the Chinese standard "Jewelry and Jade name" (GB/T 16552-2017), agate is a variety of jade in quartz jade.

So obviously it is a kind of agate, why it is called "Nanhong"? red can also be understood as its color. Red agate is the authentic agate, and there is the saying that "agate without red I is poor". The Chinese civilization nurtured in the past five thousand years has made the descendants of Yan Huang have a special fondness for red. She is not only the embodiment of passion, vitality and jubilation, but also the embodiment of evil spirits, wealth and sustenance for a better life.

Where does the "South" of "Nanhong" start? according to experts, it may be named because of the place of origin. The specific producing area of "Gu Nanhong" is only Yunnan, and the most representative producing area is the agate Mountain in Baoshan, Yunnan. As Xu Xiake wrote at that time, "on the dangerous cliff, rattan trees fall down, cut the cliff and break out rocks, then agate is embedded in it. The color of the moon is white and red, all of which are not very big, just like a fist, which is also its vine. Then in depth, the melon is as big as a rise, round as a ball, hanging as a ups and downs, but not glued to the stone, there is water to raise it, its crystal is tight, different from the regular vine, the top grade of this agate, can not be suddenly encountered, its constant accumulation and the market in people, all chisel vine income. " What we should know most is that "its color is white and the moon is red, all of them are not very big, just like a fist, this is its vine," which is the most key feature of "Nanhong".

The riddle of the formation of "South Red onyx"

"South red agate" is mainly produced in Baoshan area of Yunnan Province and Liangshan area of Sichuan Province. A small amount of output is also found in Diebu area of Gansu Province, but the output is relatively small, and the quality is not very good. Baoshan area of Yunnan Province is a producing area of "South Red agate" with a long history, but because its "South Red" agate has many cracks and defects and small size, it is unable to perform carving skills, and with years of mining, its mining area resources have been gradually exhausted, so it gradually withdrew from the market. The "southern red agate" in Liangshan, Sichuan is mainly produced in Meigu County, Liangshan Prefecture. The agate ore is sought after by the market because of its ruddy color, good integrity, large volume and high quality, and its economic value has been rising in recent years. At present, the mainstream "southern red agate" in the market are produced in Liangshan area of Sichuan Province.

Since its rediscovery, academia and collectors have set off an upsurge in the study of "southern red agate", constantly exploring the mystery of its formation and unveiling her layers of veil. At present, there is not an accurate national standard for "southern red agate". It is usually identified by the standard of agate. The content of silicon dioxide in "southern red agate" is more than 95%, and its composition is the same as that of ordinary agate. they are all cryptocrystalline mineral aggregates composed of quartz. The optical properties of agate, such as hardness 6.5-2.7 and relative density 2.6-2.7, are also suitable for southern red agate.

The biggest difference between "southern red agate" and ordinary red agate is that "southern red agate" has a glossy oil, delicate texture and unique red. When the "southern red agate" is observed in the bright light, you can see that there are many red dots ("cinnabar spots" in the jargon), and the red presented by the "southern red agate" is formed by the aggregation of these dots. Ordinary onyx does not have this feature, but the relatively dark color of "southern red agate" cannot be seen because the light cannot penetrate through it.

The "red" in "South Red onyx" should be colored by some mineral. The main chemical composition of "Nanhong" is silicon dioxide, mineralogically speaking, the main mineral composition is quartz (more than 90%), and quartz itself is colorless, so it is speculated that the coloration of "Nanhong" is caused by one or more of the remaining chemical components. Studies have shown that agate can vary in color from light to dark because it contains trace amounts of iron, cobalt, titanium, nickel and other elements. "Nanhong" is colored by trivalent iron ion elements. the chemical composition of fine red particles is iron trioxide, that is, hematite, because trivalent iron ions have high oxygen fugacity in agate production environment and can not combine with silicon under water-rich conditions. form silicate minerals, resulting in trivalent iron ions not entering the silica crystal, but dissociating in the ion gap in the form of iron trioxide particles. Therefore, there are two ways of coloring "Nanhong": one is that the mineral inclusions of hematite are suspended in the quartz particles in a round shape, and the other is caused by the leaching of cryptocrystalline hematite mixed with the "Nanhong" particles.

Taking the Nanhong agate deposit in Meigu County, Liangshan Prefecture, Sichuan Province as an example, we can try to explore the formation process of Nanhong.

First, the primary ore-forming process: about 250 million years ago (late Permian), basaltic magma surged along the mantle plume from the depths of the earth's crust and ejected to the surface along deep faults. Because the magma is relatively viscous, it can form large bubbles and can carry a variety of metal ions from the center of the mantle. The magma flows slowly, and the bubbles gradually rise and gather in the upper part of the basaltic magma layer. The rich steam, water, hydrothermal and silicon, iron, chromium and other elements of basaltic magma gradually accumulate in these bubbles and form agate around a particle in a circle. With the change of temperature, pressure and chemical properties of basaltic magma, the agate in the stomata forms different circles, and the different thickness of each layer represents a relatively stable period of basaltic magma. Because the magma is rich in silicon and oxygen, the hydrothermal solution is immersed into the agate in the lower magmatic pores or caves, and the bivalent iron in the agate is fully oxidized to trivalent iron at high temperature to form fine hematite particles, thus forming a "southern red agate". In this process, the flow of the upper magma promotes the flow of the unconsolidated magma in the lower layer, and causes the unconsolidated "southern red agate" to deform or produce fissures, and the "southern red agate" produces flow plastic deformation due to the action of high temperature. so that it has a fibrous structure. Because the basaltic magma belongs to polycyclic continuous eruption, the repetition of the above process can form multi-layer "southern red agate" deposits, all of which are located at the top of the basalt layer with similar composition.

The second is the ore-forming process: at the end of the late Permian, after the magma stopped erupting and consolidated mineralization, the Xichang area continued to uplift, so that the top of the uppermost basalt was first weathered and eroded by air and running water. The "southern red agate" in the basalt was weathered and denuded, but because the basalt was hard and the weathering and denudation rate was slow, only the upper basalt was destroyed, so that the "southern red agate" was moved away from the original place. The "southern red agate" on the top of a large number of lower basalts is buried deep in situ. Because of its low topography and easy to accept deposition, the Meigu basin form