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[Chemical composition] The chemical composition is complex and variable. Al 3+ and Fe 3+ Si in the tetrahedral sheet are the main cause of layer charge generation. On the one hand, the charge compensation depends on Al 3+ and Fe 3+ on the octahedral sheet, and on the other hand, the interlayer cation, the interlayer cation is mainly Mg, and there may be Ca, Na, K, (H 3 O). + , you can also have Rb, Cs, Li, Ba, etc. The amount of water in the interlayer depends on the cation hydration ability of the interlayer and the temperature and humidity in the environment. Mg 2+ with high hydration ability, under normal temperature and humidity, the unit chemical formula can contain 4 to 5 water molecules. However, when the cation is Cs + with weak hydration ability, it is almost free of water molecules. When the interlayer water content is maximum, it is equivalent to about a bilayer.
[Crystal structure] monoclinic system; 
; a 0 = 0.53 nm, b 0 = 0.92 nm, c 0 = 2.89 nm; β = 97°; Z = 4. The crystal structure is a TOT type, which may be a trioctahedral type or a dioctahedral type. The interlayer water molecules can be divided into two parts: one part is formed around the ligand octahedral cations, hydrated complex ion [Mg (H 2 O) 6 ] 2+  form; free in the other part. The water molecule layer and the bottom surface of the unit layer are maintained by hydrogen bonding. The size of c 0 is related to the content of water molecules and the structure of water molecules. The sample is slowly heated and dehydrated. The layer structure of water molecules in the interlayer consists of saturated double-layer water molecules → unsaturated double-layer water molecules → mutated double-layer water molecules → The single layer of water molecules → complete dehydration, c 0 will gradually decrease until the value of c 0 in the mica structure. The partially dehydrated vermiculite can reabsorb, but the completely dehydrated vermiculite is difficult to absorb water.
[Configuration] converted from multiple coarse vermiculite biotite, phlogopite and the like, to retain the mica flake crystalline form (FIG. G-46), and the main body of trioctahedral; fines to those with other clay minerals earthy Mixed together, it is extremely difficult to distinguish, the clay-grade vermiculite is mostly dioctahedral and widely distributed in the soil.
Figure G-46 vermiculite crystal
[Physical properties] brown, brown, gold, bronze yellow, sometimes greenish; biotite gloss than weak, often oil sheen or pearl luster. The cleavage {001} is complete, and the cleavage film is slightly or not elastic. Hardness 1 to 1.5. The relative density is 2.4 to 2.7. When it is hot, the volume expands and bends like a leech, which is light golden or silvery white and metallic luster. The expansion is caused by the pressure generated when the water molecules in the interlayer become vapor, so that the structural layer is rapidly opened. After expansion, the volume increases by 15 to 25 times, and even up to 40 times. The relative density is reduced from 2.34 to 2.7 to 0.6 to 0.9.
[Cause and occurrence] It is mainly formed by hydrothermal alteration or weathering of biotite or phlogopite. It can also be formed by the metamorphism of the acidic rock by the basic rock.
[Identification characteristics] The coarse particles are similar to mica, but they are distinguished by their inelasticity and heat expansion; those of fine particles should be identified by X-ray and differential thermal analysis.
[Main use] Expanded vermiculite has good sound insulation, heat insulation, insulation, chemical stability and other properties, so it is widely used in the construction industry and various industrial sectors as lightweight, thermal insulation, heat insulation, sound insulation, fireproof and other materials. . Vermiculite has good cation exchange and adsorption properties. It is used in agriculture for soil improvement, fertilizers, pesticides, etc., and can be used as an adsorbent for waste and pollution in environmental protection.
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