Magnesite: This is a stone that can be used to weave cloth?

Brucite is named in honor of Archibald Bruce (1777-1818), a mineralogist. Brucite is also known as magnesia hydroxide. As the name suggests, the main chemical composition of magnesia is Mg(OH)2. The magnesium ion (Mg2+) in the composition can be replaced by isomorphous ions such as iron (Fe2+), manganese (Mn2+), and zinc (Zn2+). Among them, manganese oxide (MnO) can reach 18%, iron oxide (FeO) can reach 10%, or zinc oxide (ZnO) can reach 4%; it can form manganese magnesia, iron magnesia, zinc magnesia, manganese zinc magnesia and other variants. The isomorphous mixing and replacement of iron and manganese ions will make the color of the mineral darker and the density higher. Because brucite contains structural water, when it reaches 340℃, the mineral begins to gradually absorb heat and decompose to obtain magnesium oxide and water.

Brucite is a trigonal mineral with a layered structure. The crystals are plate-like or leaf-like. The aggregates are often plate-like, flaky, rounded, or irregularly granular. If they are parallel fibrous aggregates, they are called nemalite. Brucite is white or off-white in color. When mixed with iron or manganese, it becomes green, yellow, or reddish brown in varying shades. It has a glassy luster on the fresh surface and fracture, and a pearly luster on the cleavage surface. Nemalite has a silky luster and is transparent. It has a hardness of 2.5 and a relative density of 2.3-2.6. It has a very complete cleavage. The nemalite flakes are flexible and pliable.

Brucite mineral specimen (one of the world's rock and mineral specimens)

Brucite is formed by the hydrolysis of soluble magnesium-containing compounds in a strong alkaline solution. It is a secondary change product of the action of alkaline solution on magnesium silicate. It is a typical low-temperature hydrothermal alteration mineral, often derived from periclase or serpentine.

Brucite is widely used in fireproof materials, papermaking industry, production of magnesium oxide, magnesium chloride, environmental protection and other fields. Brucite can be used to make flame retardants (a kind of auxiliary agent that can slow down the burning of combustibles or flammable materials when they encounter a fire source or after they catch fire) and magnesium high-temperature refractory materials. The high-grade halogen-free flame retardant prepared with it is an environmentally friendly and safe flame retardant. Due to its layered structure effect, it has both filling and flame retardant functions. The fire-retardant coating made of brucite has the characteristics of light bulk density, good decorativeness, strong weathering resistance, good fire resistance, and no peeling after fire. It can be used for surface coatings of ships, high-end residential buildings, etc.

There are many records of a kind of cloth called "fire-washed cloth" in ancient China. For example, "Liezi·Tangwen" says: "Fire-washed cloth must be thrown into fire after washing." As the name suggests, it is a cloth that is washed with fire instead of water to remove dirt. It is now generally believed that the material for making fire-washed cloth is mainly asbestos fiber, because asbestos is non-flammable. In addition to asbestos, fibrous brucite can also be used to make "fire-washed cloth". Its important characteristics are that it can release a large amount of water vapor at a lower temperature, and the MgO generated by decomposition also has high activity and good heat resistance. In addition, brucite has obvious flexibility and flexibility (the property that minerals are deformed by force and cannot return to their original state after the force is lost). These characteristics make it an excellent rock and mineral raw material for weaving. Comparing asbestos and brucite, modern research shows that asbestos is very harmful to the human body and the environment, and has been identified as a confirmed carcinogen by the International Agency for Research on Cancer, while brucite is safe and environmentally friendly and is an excellent fireproof material.

A sealed aggregate of granular brucite (one of the world's rock and mineral specimens)

It is known that brucite has the highest magnesium content among magnesium minerals. As one of the important raw materials for extracting magnesium, it is a precious high-magnesium non-metallic mineral. In addition, brucite can be used as a filler in the papermaking industry. It can be used as a safe, non-toxic, harmless and green neutralizer in the treatment of acidic wastewater; it can be used as a flue gas desulfurization agent in air treatment to reduce the pollution of harmful components in flue gas to the atmosphere.

Sometimes you can see brucite in the jewelry and crafts market, but it is more often used as an imitation of Shoushan stone and Hetian jade. Because of its dense block shape, uniform texture, fine and lustrous appearance, good transparency, high ornamental value, and some with striped patterns, brucite can be carved into crafts. Some crafts are difficult to distinguish from high-grade Shoushan stone by relying only on appearance characteristics. At this time, it is necessary to use analytical testing instruments such as X-ray infrared spectroscopy and X-ray powder diffraction analysis to help identify them.

The distribution of brucite deposits in the world is limited, and the scale of deposits is generally small, mainly concentrated in Russia, the United States, Pakistan, Canada, North Korea, Norway, etc. my country's brucite resource reserves are medium-sized, and the main deposits are distributed in Fengcheng, Kuandian, Liaoning, Ji'an, Jilin, Ningqiang, Shaanxi, Qilian Mountain, Qinghai, Shimian, Sichuan, Xixia, Henan, etc.

Appendix: The minerals introduced in this issue belong to the world's rock and mineral specimens, which are treasured in the Earth Science Museum of Kunming University of Science and Technology. They are one of the geological teaching specimens customized in the early years of the Republic of China. Many specimens were collected from the original naming places of rocks and minerals, classic mining areas and stratigraphic sections. Some mineral deposits no longer exist after long-term mining, so many collected specimens cannot be recovered. This set of specimens moved south during the Anti-Japanese War, and after several twists and turns, they were preserved in Kunming University of Science and Technology through the National Southwest Associated University. They have been preserved almost intact to this day, witnessing the formation and development of China's modern geological disciplines and earth science education, and have important scientific research, historical and cultural relic value.

Written by: Zhu Jun, Shen Cen, Wang Lei

Scientific Advisor: Zhang Shitao

Photographed by: Yang Yuchen

Supporting institution: College of Land and Resources Engineering, Kunming University of Science and Technology