This shiny "zinc" may be less famous, but its "appearance" is not inferior to diamonds

In nature, lead and zinc not only have similar properties, which led the ancients to call zinc "wo lead", but the two often coexist together. For example, in Yunnan, Inner Mongolia, Gansu, Guangdong, Hunan and Guangxi in my country, there are large-scale lead-zinc mines. Lead-zinc mine is not the name of a specific mineral, but a deposit rich in lead and zinc.

Among lead ores, galena is the most important, with the highest lead content, the widest distribution, and the most important. Among zinc ores, sphalerite is the most important. The main component of sphalerite is zinc sulfide, with a zinc content of up to 67.1%. It is mainly produced in medium-temperature hydrothermal (200-300℃) polymetallic sulfide deposits, and is often oxidized on the surface to form smithsonite (which is composed of zinc carbonate and can also be used as a mineral raw material for extracting zinc).

Yunnan Lanping Lead-Zinc Mine (Picture from the Internet, deleted if infringed)

As an important zinc-containing mineral, sphalerite has a large output and a wide distribution. It is produced all over the world and has beautiful crystals. The crystals of sphalerite mainly have tetrahedron, cube, and rhombic dodecahedron forms, and gather together to form crystal clusters. The crystal morphology is affected by temperature conditions. For example, rhombic dodecahedron is the majority under medium and low temperature conditions. Sphalerite crystals without impurities are transparent and colorless, but in actual situations, its color often changes from light (light yellow, yellow, etc.) to dark (brown, black, etc.) due to iron. In addition to iron, sphalerite often contains rare elements such as manganese, cadmium, indium, thallium, gallium, and germanium. These elements not only affect the crystal color of sphalerite, but also make it a raw material for extracting these elements in addition to extracting zinc.

Sphalerite crystal

The iron element not only affects the color of its crystal, but also its hardness and specific gravity. The Mohs hardness of sphalerite is between 3.5 and 4.0, and the specific gravity is between 3.9 and 4.2. Sphalerite, which becomes darker in color as the iron content increases, is mainly used as an industrial raw material. Among the large amount of sphalerite, a small number of sphalerites have intact crystals, high transparency and beautiful colors. Such sphalerite has another use - as a gem.

Large sphalerite specimen in the collection

If industrial-grade sphalerite mainly reflects "zinc", then gem-grade sphalerite mainly reflects "sparkle". The brilliance of diamonds is well known, but gem-grade sphalerite is more dazzling than diamonds. The reason is that sphalerite crystals have strong fire, which is determined by the dispersion value. The dispersion value of sphalerite is as high as 0.156, which is higher than the 0.044 of diamond. If the dispersion value is higher than diamond, it may not be more dazzling than diamond, but sphalerite has another major feature, which is the refractive index of 2.37, which makes it have the same diamond luster as diamond. These two points make it not inferior to diamond in appearance.

Gem-grade sphalerite crystal (picture from the Internet, please delete if infringed)

However, as a gemstone, the Mohs hardness between 3.5 and 4.0 and the complete cleavage are flaws (easy to break and difficult to process), which means that sphalerite can only be used as a rough crystal or finished product faceted for viewing, but not suitable for wearing. However, high-quality gem-grade sphalerite is still very rare and precious, and is favored by collectors. For example, the heavyweight sphalerite collection in our museum is produced from the Shuikoushan lead-zinc mine in Hunan, with a total weight of 12 tons. The three-dimensionally preserved surrounding rock has tens of thousands of complete sphalerite crystals growing on each side, and they are continuous in pieces, forming crystal clear crystal clusters, which are extremely rare and precious specimens.

Large sphalerite specimen in the collection