Mica
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Mica

MGT Mineral Company as a major producer, supplier and exporter of several minerals and materials in the Middle East, is located in Iran. MGT Mineral Company has a lot of experience in exporting and is active in case of Iran Mica supplying.

Humans have been using mica for millennia. Mica was first mined in India about 4,000 years ago, where it was used primarily in medicines, and some Hindu physicians still incorporate biotite mica into medicines today. Early civilizations also used mica for decorations, as windows and as surfaces on which to draw or paint. Maya temples were decorated with mica pigments, which were incorporated into the stucco to make it sparkle in the sun. In North America, ancient inhabitants adorned gravesites and burial mounds with animal figures made of mica.

The word “mica” comes from the Latin word micare, meaning to shine or flash, an allusion to mica’s ability to reflect and refract light. “Mica” represents 37 phyllosilicate minerals that have a layered or platy texture. These mica minerals all have a crystalline structure that forms layers that can be split into thin sheets, a physical property called perfect basal cleavage.

Resources of scrap and flake mica are available in granite, pegmatite, schist, clay and placer deposits in many countries, including Brazil, India, Madagascar and Russia. Sheet mica occurs most commonly in pegmatites, a coarse-grained granitic igneous rock that forms under non-equilibrium conditions of temperature and pressure.

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What is Mica?

Mica is the name for a family of 37 phyllosilicate minerals that have a platy or layered structure. All micas form flat hexagonal monoclinic crystals with plane angles of 60° and 120° on the basal system and indicate perfect basal cleavage. This permits them to split into optically flat films. Their different physical properties and chemical compositions distinguish the micas from each other. The commercially important Mica minerals are:

•Muscovite – potassium Mica (colorless to pale green and ruby)

•Phlogopite – magnesium Mica (pale yellow to dark brown)

•Vermiculite – hydrated biotite or magnesium-Iron Mica (bronze yellow flakes)

These are the most commercially important micas. Lepidolite is also mined for its lithium content.

 

Physical Properties of Muscovite
Chemical Formula KAl2(AlSi3O10)(OH)2
Cleavage Perfect on {001}
System Monoclinic
Color White, Gray, Silver white, Brownish white, Greenish white
Density 2.82 g/cm3
Diaphaneity (Transparency) Transparent to translucent
Fracture Brittle - Sectile - Brittle fracture with slightly sectile shavings possible
Tenacity Elastic
Habit Foliated - Two dimensional platy forms.
Massive - Lamellar - Distinctly foliated fine-grained forms.
Micaceous - Platy texture with "flexible" plates.
Hardness (Mohs) 2-2.5 - Gypsum  -Finger Nail
Luminescence Non-fluorescent
Luster Vitreous (Glassy)
Streak White
Magnetism Nonmagnetic

Biotite, a magnesium-Iron Mica which has dark brown to black color, despite of presenting in greater range of geological environments than any other micas, does not have commercial attraction in its own right. However, if biotite is altered to hydrobiotite and then vermiculite, it becomes commercially considerable.

 

The value of muscovite Mica lies in its unique physical characteristics. The crystalline structure of Mica has a unique property that can be split or delaminated into thin sheets. These sheets are transparent to opaque, flexible, resilient, dielectric, reflective, refractive, chemically inert, infrared and radio frequency transparent, insulating, lightweight and hydrophilic. Mica is stable when exposed to, extreme temperatures, moisture, light and electricity.

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The value of muscovite Mica lies in its unique physical properties. The crystalline structure of Mica forms mineral layers that can be split or delaminated into thin sheets. These sheets are flexible, transparent to opaque, resilient, reflective, refractive, dielectric, infrared and radio frequency transparent, chemically inert, insulating, lightweight and hydrophyllic. Mica is stable when exposed to electricity, light, moisture and extreme temperatures.

 

Physical Properties of Phlogopite
Chemical Formula KMg3(AlSi3O10)(OH,F)2
Cleavage Perfect on {0001}
System Monoclinic
Color Brown, Gray, Green, Yellow, Reddish brown
Density 2.8 g/cm3
Diaphaneity (Transparency) Transparent to translucent
Fracture Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern
Tenacity Flexible
Habit Lamellar - Thin laminae producing a lamellar structure.
Micaceous - Platy texture with "flexible" plates.
Scaly - Morphology like fish scales.
Hardness (Mohs) 2-2.5 - Gypsum  -Finger Nail
Luminescence Fluorescent, Short UV=Straw to Lemon Yellow, Long UV=Weak Blue-white to blue-gray
Luster Vitreous - Pearly
Streak White
Magnetism Nonmagnetic

 

Physical Properties of Vermiculite
Chemical Formula (Mg,Fe,Al)3((Al,Si)4O10)(OH)2 • 4H2O
Cleavage {001} Perfect
System Monoclinic
Color Colorless, Green, Gray white, Yellow brown
Density 2.5 g/cm3
Diaphaneity (Transparency) Translucent
Fracture Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern
Habit Lamellar - Thin laminae producing a lamellar structure.
Scaly - Morphology like fish scales.
Hardness (Mohs) 1.5-2 - Talc-Gypsum 
Luster Vitreous - Pearly
Streak Greenish White
Magnetism Nonmagnetic

Mica Occurrence

A discussion of the occurrence of muscovite Mica means practically a discussion of the occurrence of pegmatite, for Mica is found in a great many types of this rock. Pegmatite occurs as intrusions of bulky masses, in veinlike or dikelike sheets, in lenses, and in various irregular-shaped deposits. The deposits range in thickness from a small fraction of an inch to more than 200 feet. The larger masses resemble granitic intrusions. Some of the smaller deposits are more like veins.

Micas are a group of complex hydrous aluminosilicate minerals, with the general formula X2Y4-6Z8O20 (OH,F)4 where X is mainly K, Na or Ca; Y is mainly Al, Mg or Fe; and Z is mainly Si or Al. Micas exhibit a number of characteristic physical properties. They form monoclinic crystals with perfect basal cleavage which enables them to split into thin, flexible and elastic sheets. Micas also have good electrical and thermal insulating properties, toughness, and good reflective and refractive properties. 

Of the 37 varieties of mica, the most common are biotite (magnesium–iron), muscovite (potassium–aluminium), phlogopite (potassium–magnesium), lepidolite (potassium–lithium) and zinnwaldite (lithium–iron). Vermiculite, which is sometimes referred to as a mica, is an alteration product of biotite or phlogopite and is dealt with separately (see chapter on vermiculite). Muscovite, phlogopite and lepidolite are the only mica minerals of economic importance. Lepidolite is discussed separately in the chapter on lithium.

Mica is produced commercially in two main forms, sheet mica and flake (scrap mica).

Sheet mica: Sheet mica occurs in crystal forms (known as ‘books’) which are several centimetres in diameter and can be split into thin sheets.

Flake, scrap or ground mica: Flake, scrap or ground mica is fine-grained mica ground for use in a wide variety of applications. In the past, flake mica was produced as a waste product from processing sheet mica hence the name ‘scrap mica’. However, today flake mica is largely a by-product from mining pegmatites or alaskites for feldspar and other minerals.

Sheet mica is graded according to colour, visual quality and the maximum useable rectangle which can be cut from a single lamina. It is commonly divided into four categories that include block mica; thins; film mica; and splittings. Flake mica is graded primarily on the basis of the grinding technique used and the resultant particle size.

 

Mica Usages

The United States is the leading supplier of mica, with about 46% of the world’s production. The US produces only ground muscovite. The only significant production of phlogopite is in Canada and Finland, which together account for about 15% of total worldwide mica output. India produces 80% of the world’s sheet mica. In the US fully half the mica produced is used in wallboard joint cements. Other major end uses are coatings, plastics, and well drilling fluids.

Drilling fluids: Coarse, hammermilled (+10 mesh) mica is used in waterbased oilwell drilling fluids to prevent fluid loss into porous rock formations. The coarse mica flakes bridge openings and seal porous sections of the drill hole against loss of circulation. Mica’s platy nature also aids in the suspension of drilling fluid solids and cuttings.

 

Joint cements: Fine dry-ground (fluid energy-milled) muscovite is used in drywall joint compounds, where it contributes to consistency and workability, smooth surface finish, and resistance to shrinkage and cracking. 

 

Coatings: Fine-ground, -325 mesh and micronized mica grades are used in paint as a pigment extender and for dry film reinforcement. The inert, platy mica improves suspension stability, controls film checking, chalking, shrinkage, and blistering, improves resistance to weathering, chemicals, and water penetration, and improves adhesion to most surfaces. Coarser grinds are used in textured paints, and wet-ground mica is used in high quality exterior house paints. High aspect ratio grades are preferred for porous surface sealers to seal pores, control penetration, and reduce sagging and film cracking. Automotive paints use high aspect ratio mica to achieve a metallic effect either as is, or after conversion to pearlescent pigments by surface coating with metal oxides.

 

Plastics: Finely ground, -325 mesh and micronized micas are used in plastics to improve electrical, thermal, and insulating properties. Mica is considered the most effective mineral for reducing warpage and increasing stiffness and heat deflection temperature in plastics. In general, mica reinforces crystalline better than amorphous polymers. Best results are obtained with nonpolar polymers when mica is pretreated with a coupling agent to improve wetting. Mica is used in both thermoplastics and thermosets. Its largest single use is in polyolefins, even though it requires stabilizers to prevent degradation of polypropylene. Both muscovite and phlogopite micas are used in plastics, with high aspect ratio grades preferred for their superior reinforcement properties.

 

Other uses: Ground mica is used as an asbestos substitute in certain thermal boards, brake linings, gaskets, and cement pipes, as a filler and nonstick surface coating for roll roofing and asphalt shingles, as a mold lubricant and release agent in the manufacture of tires and other molded rubber goods, as a flux coating on welding rods, and as a pearlescent pigment in wallpapers.

 

 

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