Liaoning Xinda Talc Group Co., Ltd. - Yang Yongli
1、 Introduction
Talc, magnesite, chlorite, and calcite are common minerals in nature, and their structural differences directly determine their physical properties and industrial applications. Xinda talc, as one of the important fillers in inorganic powders, is often associated with vein minerals such as chlorite and magnesite. Talc and chlorite, as layered silicate minerals, have significant surface anisotropy that affects mineral processing efficiency. Calcite and magnesite are both carbonate minerals, but the difference in cations leads to different chemical activities. Liaoning Xinda Talc Group R&D Center systematically compares the crystal structure characteristics of four minerals, analyzes the underlying mechanisms of their physical property differences, and explores the impact of structural differences on industrial applications.
2、 Analysis of Mineral Structure Characteristics
1. Talc (Mg ∝ Si ₄ O ₁₀ (OH) ₂)
1.1 Crystal structure: monoclinic crystal system, 2:1 type layered silicate, triakis octahedral structure. The tetrahedral layer of silicon oxide and the octahedral layer of magnesium oxide are connected by a shared oxygen atom to form TOT type structural unit layers, which are only maintained by van der Waals forces between the layers.
1.2 Physical properties: flaky or scaly aggregates, parallel cleavage, hardness 1-1.5, specific gravity 2.7-2.8g/cm3, with a smooth texture. There are no chemical bonds between layers, with strong surface hydrophobicity and good natural floatability.
1.3 Industrial characteristics: There are significant differences in the morphology of talc from different origins (such as sheet-like in Haicheng, Liaoning and plate-like in Guangxi), which affects its applications in plastics, coatings, papermaking, ceramics and other fields.
2. Magnesite (MgCO3)
2.1 Crystal structure: Triangular crystal system, calcite type structure, formed by alternating arrangement of Mg ² ⁺ and CO VNet ² ⁻ to form layered carbonate structure.
2.2 Physical properties: often in the form of grains or cryptocrystalline blocks, with complete cleavage, hardness of 3.5-4.5, specific gravity of 2.9-3.1 g/cm3. When containing elements such as Fe and Co, there is a significant color change and a glassy luster.
2.3 Structural stability: The ionic bond structure decomposes into MgO and CO ₂ at high temperatures (>600 ℃), and the high temperature resistance comes from strong ionic bonds.
3. Chlorite (Mg, Fe, Al) 6 (Si, Al) 4O10 (OH) 8
3.1 Crystal structure: monoclinic crystal system, 2:1 layered silicate, with structural unit layers consisting of negatively charged tetrahedral aluminum (magnesium) oxide octahedral layers (2:1 layers) alternately stacked with positively charged magnesium hydroxide layers. The Y site is mainly composed of Mg, Fe, and Al, while the Z site is composed of Si and Al.
3.2 Physical properties: pseudo hexagonal or plate-like, with completely parallel cleavage, hardness of 2-3, specific gravity of 2.6-3.3 g/cm3. The color changes from light green to dark green with increasing Fe content, and the interlayer hydrogen bonds enhance the structural stability.
3.3 Surface characteristics: The bottom surface has weak hydrophobicity, and the end surface has hydrophilicity due to broken bonds. The isoelectric point pH is about 3-6.
4. Calcite (CaCO ∝)
4.1 Crystal Structure: Triangular crystal system, deformed NaCl type structure, with Ca ² ⁺ and CO ∝ ² ⁻ arranged alternately along the third symmetry axis, forming a rhombohedral crystal cell.
4.2 Physical properties: Commonly found rhombohedral or hexagonal columnar crystals, with complete cleavage, parallelism, hardness of 3, specific gravity of 2.71g/cm3, and violent foaming when exposed to dilute HCl.
4.3 Chemical activity: Ca ² ⁺ sites have high density, strong surface hydrophilicity, and are prone to electrostatic interactions with collectors
3、 Comparison of structural differences with talc
1. Crystal chemical composition
Cation type: Magnesite (Mg ² ⁺) and calcite (Ca ² ⁺) are carbonate minerals with a single cation;
Chlorite (Mg ² ⁺, Fe ² ⁺, Al ³ ⁺);
Talc (Mg ² ⁺) is a silicate mineral with diverse cations. In the octahedral structure of talc, the octahedral voids are completely filled with Mg ² ⁺; Due to isomorphic substitution of chlorite, some gaps are not filled, resulting in interlayer charge imbalance.
2. Interlayer forces and physical properties
Bonding mechanism: The interlayer of talc is van der Waals force, which is extremely weak and prone to sliding, resulting in low hardness and smoothness.
The hydrogen oxygen magnesium layers between the chlorite layers are connected by hydrogen bonds, with strong bonding strength and slightly higher hardness than talc, but still lower than magnesite and calcite.
The interlayer ionic bonds (Mg ² ⁺ - CO ∝ ² ⁻, Ca ² ⁺ - CO ∝ ² ⁻) between magnesite and calcite endow them with high hardness, but the cleavage is still complete.
3. Crystal symmetry and cleavage characteristics
3.1 Symmetry: Magnesite and calcite belong to the trigonal crystal system, with high symmetry; Chlorite and talc belong to the monoclinic crystal system with low symmetry.
3.2 cleavage direction: parallel and complete cleavage of talc, parallel and complete cleavage of chlorite, parallel and complete cleavage of magnesite and calcite.
3.3 The cleavage surface of talc has no chemical bond breakage and strong surface hydrophobicity; The cleavage plane of chlorite has slightly higher hydrophilicity due to hydrogen bonding.
4. High temperature stability and industrial applications
Talc only undergoes structural damage above 800 ℃ and is suitable for high-temperature lubricants; High temperature decomposition of magnesite into MgO, used for refractory materials; Due to interlayer hydrogen bonding limitations, chlorite is prone to dehydration and metamorphism at high temperatures.
4、 Application and Prospect
Liaoning Xinda Talc Group R&D Center is conducting research and development on the basic application of talc, which is soft in nature. Low Mohs hardness, suitable for lubricants, plastics, coatings, ceramic fillers; Research has shown that the higher the silicon content, the better its chemical stability, the completed sheet-like structure, and the greater its resistance to acid and alkali, salt spray, and the greater its potential to block corrosive media; In addition, research conducted by the R&D center of Liaoning Xinda Talc Group has shown that the sheet-like structure of talc gives it a strengthening and anti settling effect in coatings; Chlorite has potential applications in the fields of ceramics and environmental protection; Calcite is used in building materials and chemical industry.
5、 Conclusion
The structural differences between Xinda talc and magnesite, chlorite, and calcite are mainly reflected in cation composition, interlayer forces, crystal symmetry, and cleavage characteristics. The interlayer van der Waals force of talc endows it with extremely low hardness and hydrophobicity, while the ionic bond structure of magnesite and calcite makes it resistant to high temperatures but highly chemically active. The hydrogen bond interlayer structure of chlorite falls between the two in terms of stability and flotation behavior. These differences directly determine the physical properties and industrial applications of minerals. In the future, it is necessary to combine crystal chemistry and surface science to further reveal the intrinsic relationship between mineral structure and properties.
References
1. Liaoning Xinda Talc Group. Composition and structural characteristics of talc [EB/OL]. http://www.xindatalc.com/baoding_industry/395.html, 2022.
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3. Mineral Expert. Magnesite - Complete Mineral Overview[EB/OL]. https://mineralexpert.org/article/magnesite-magnesium-carbonate-mineral-overview, 2019.
4. Magnesite (a magnesium carbonate mineral) _ Encyclopedia [EB/OL] https://m.baike.com/wiki/ Magnesite, without date
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6. PCI Magazine. Talc Shape and Form Meet Function[EB/OL]. https://www.pcimag.com/articles/83323-talc-shape-and-form-meet-function, No date
7. Answers.com. What elements in Talc[EB/OL]. https://www.answers.com/earth-science/What_elements_in_Talc, 2024.
