Kaolinite is a clay mineral from the group of aqueous aluminum silicates .
| Kaolinite | |
|---|---|
 | |
| Formula | Al 4 [ Si 4 O 10 ] ( OH ) 8 |
| Physical properties | |
| Colour | White, brownish, grayish, pale yellow, greenish |
| Trait color | White |
| Shine | Sallow (Dull) |
| Transparency | Transparent, translucent |
| Hardness | 1,5-2 |
| Cleavage | Perfect on {001} |
| Density | 2.6 g / cmΒ³ |
| Syngonia | Triclinic [1] |
| Refractive index | 1,56 |
The chemical composition of Al 4 [Si 4 O 10 ] (OH) 8 ; contains 39.5% Al 2 O 3 , 46.5% SiO 2 and 14% H 2 O.
It is named after the place of discovery near the village of Gaolin ( Chinese ι«ε² ) near the city of Jingdezhen in southeast China.
It forms earthy masses in which small hexagonal crystals are detected under high magnification under an electron microscope. It crystallizes in triclinic syngony [1] .
Kaolinite is the main component of many clays . It is formed during kaolinization (weathering and hydrothermal change of feldspar rocks).
Content
Chemical Structure
The crystal structure of kaolinite is based on infinite sheets of Si β O 4 tetrahedra , which have three common oxygen and are connected in pairs through free vertices with aluminum and hydroxide. These sheets are interconnected by weak bonds, which leads to a very perfect cleavage of kaolinite and the possibility of various overlays of one layer on another, which, in turn, leads to some change in the symmetry of the entire crystalline structure.
Chemical Properties
When heated to 500β600 Β° C, kaolinite loses water, and at 1000β1200 Β° C it decomposes with the release of heat, giving first sillimanite and then mullite ; This reaction forms the basis of ceramic production.
Physical Properties
The layered structure of kaolinite gives minerals based on it ( clays and kaolins ) a plasticity property.
Mineralogical hardness scale 1; density 2540β2600 kg / mΒ³; greasy to the touch.
Usage
About 50% of all mined kaolinite is used in the manufacture of paper for coating and as a filler.
In the ceramic industry, it is used to create engobe and glaze .
Kaolinite is also used in pharmaceuticals, as a food additive , in toothpastes (as a light abrasive material), in cosmetics (called βwhite clayβ) and many other areas.
Varieties
- Podzolit (Podsolit) - close to kaolinite mud fraction of podzol [2]
Notes
- β 1 2 Young RA Verification of the Triclinic Crystal Structure of Kaolinite // Clays and Clay Minerals. - 1988. - T. 36 , No. 3 . - S. 225-232 . - ISSN 0009-8604 . - DOI : 10.1346 / CCMN.1988.0360303 .
- β A. A. Rode. Formation of podzolic soils // Soils of the USSR. T. 1. M., L .: Publishing house of the Academy of Sciences of the USSR, 1939.S. 157-185.