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It says that 99% of elements in earth's crust is consist of O, Si, Al, Fe, Ca, Na, K, Mg in descending order of content.
Mica is one of the pyrocrystalline igneous rocks containing these elements in a specific ratio and is classified into phyllosilicate. The basic structure of the phyllosilicate is based on interconnected six member rings of SiO4-4 tetrahedra that extend outward in infinite sheets. Three out of the 4 oxygens from each tetrahedra are shared with other tetrahedra.
Mica exist in the strata around the world. Its constituent elements and
crystalline structure depend on the locality.
The photos below show muscovite and phlogopite.
Recently, sythetic mica has also been manufatured. |
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| Indian Muscovite |
Sri Lankan Phlogopite |
In many kinds of mica, muscovite, phlogopite and sericite are usually used
as industrial materials. Synthetic mica, which is mainly produced in Japan
and China, is mostly used in the area which demands an additional value,
such as a basic material of cosmetics and super-white pearl pigment because
of its high price.
India and China have the largest deposits of muscotive, Canada and Finnland
are the biggest producers of phlogopite. Indian mica is very good in quality
as contains bigger crystals and less impurities. Chinese muscovite and
Canadian phlogopite are composed of small crystals about 5mm and are sometimes
found mixed with silicate minerals.
The table below shows the details of majour sheet phyllosilicate. |
| Mineral |
Composition formula |
Characteristics |
| Muscovite |
KAl2(AlSi3)O10(OH)2 |
Rude ore is a brownish natural platy mineral.
Octahedral ions in a crystal are mostly occupied with Al.
Nonswelling. |
| Phlogopite |
KMg3(AlSi3)O10(OH)2 |
Phologopite is darker than muscovite and soft.
Octahedral ions in a crystal is mostly occupied with Mg.
Nonswelling. |
| Synthetic Mica |
KMg3(AlSi3)O10F2 |
Synthetic fluorophlogopite, contains no (OH) of the natural phlogopite
instead the (OH)- is fully substituted with F.
White and a little rigid. Both swelling and nonswelling types exist. |
| Talc |
Mg3Si4O10(OH)2 |
The softest mineral with Mohs hardness 1.
A white mineral composed of small crystals becoming massed together.Mostly
used in pulverized form.
Nonswelling. |
| Kaolinite |
Al4Si4O10(OH)8 |
It is produced by the chemical weathering like feldspar.Low crystallization.
A white mineral formed with molecules in several micrometers.
There is also a sythetic kaolinite. Nonswelling. |
| Montmorillonite |
(Na,Ca)0.6(Al,Mg)4Si8O20(OH)4(nH2O) |
A member of smectitite family and the main constituent of bentonite.
Highly swelling. It is used as a nanocomposite. |
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| MICA CHARACTERISTICS |
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