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Roger Weller, geology instructor                             

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Mica
Tedina Allen
Physical Geology
Fall 2007

                                                                                                           Mica
 

M31 Muscovite Mica 

 

What is Mica?
    Mica is a generic term applied to a group of complex aluminosilicate minerals having a sheet or plate like structure. It forms in flat, six sided monoclinic crystals that have perfect basal cleavage and large surfaces. It is capable of easily splitting into thin, flat films.     Chemically, mica is a complex silicate of aluminum and alkalis with hydroxyl.  Some varieties may contain impurities of iron, magnesium, lithium, fluorine, barium, manganese and vanadium.
 

    It is because of its perfect basal cleavage and its chemical and physical properties, that mica is a very valuable and desired mineral in many ways. No other substance found in nature possesses all the properties of mica.
 

Properties of Mica

    Mica possesses some of the most outstanding combinations of physical, electrical, thermal and mechanical properties which are not found in any other product.  The crystalline structure forms the layers that are so easily delaminated into sheets.  Mica is chemically inert, a non-conductor of electricity ( dielectric ), elastic, flexible, readily absorbs water ( hydrophilic ), insulating, lightweight, reflective, flat and broad ( platy ), refractive, resilient, and can range from transparent to opaque as needed.  Mica is stable when exposed to light, moisture, and extreme temperature.  It is inert to the action of water, most acids, oil, and is virtually unaffected by atmospheric action.
 

Types of Mica

    There are several different types of Mica that can vary in composition due to geologic occurrence. There are more than 20 chemically distinct mica species.  All micas have the same essential crystal structure and are easily recognizable as mica.

    There are six main important mica minerals, these are:

 

    Muscovite    ( pure potassium mica )

   http://skywalker.cochise.edu/wellerr/mineral/mica/6muscovite-peel.jpg
 

 

Paragonite  ( sodium mica )

http://skywalker.cochise.edu/wellerr/mineral/mica/6paragonite226a.jpg
 

 

Lepidolite ( lithium mica )

http://skywalker.cochise.edu/wellerr/mineral/mica/6lepidolite21.jpg
 

Phlogopite ( magnesium mica )

 

 http://skywalker.cochise.edu/wellerr/mineral/mica/6phlogopite231a.jpg
 

Biotite  ( magnesium, iron mica )

 http://skywalker.cochise.edu/wellerr/mineral/mica/6biotite1.jpg


Zinnwaldite (lithium, iron mica)

 http://www.mineralminers.com/images/zinnwaldite/mins/zinm122.jpg



 

    Out of all of the mica minerals, muscovite and biotite are the most common.  Whenever the word mica is used, it is generally thought to be muscovite that is being referred to.
 

Uses for Mica

    Mica is extremely valued by industry due to its unique properties.  Industry seems to have found use mostly from three different types of mica.
 

    Lepidolite is the source of mica from which lithium is obtained. That is the only way Lepidolite is utilized.
 

    Phlogopite is able to remain stable at a very high temperature, usually about 1000 degrees Celsius. It is because of this incredible durability, it is often used in applications in which a combination of high heat stability and electrical properties are required. However, phlogopite does not possess as much flexibility and split ability as other micas.
 

    The most widely used type of mica is Muscovite.  Muscovite has greater dielectric strength than any other insulating material.  It surpasses all other micas in dielectric strength, thermal endurance, mechanical strength, moisture resistance, transparency, flexibility, resilience, toughness, and perfection of cleavage.  It is recognized as the best mica for electrical and electronics devices.  It is the principal mica used by industry.  It is used in many ways, but is invaluable to the electrical industry.
 

    Electrically, mica not only has dielectric strength but also a uniform dielectric constant and capacitance stability, low power loss, high electrical resistivity and low temperature coefficient and capacitance. It is noted for its resistance to arcing.
 

    Thermally, mica is fireproof and non-flammable, infusible, and incombustible. Most micas can resists temperatures of about 900 degrees Celsius with no noticeable effects. It has low heat conductivity, and excellent stability.
 

    Mechanically, mica is relatively soft, flexible, and elastic and yet it is still tough. It can be hand cut, machined or die punched.
 

    Mica is usually used in two forms for most things. It is used in sheet form or ground up.  It is the sheet form that is used in so many electrical apparatus.  It is used in heating appliances, electrical control, lighting, industrial electrical needs, radios, radars, televisions, motors, generators, and transformers.  It is used to line the gauge glass of high pressure steam boilers, in optical filters, in diaphragms for oxygen- breathing equipment, missile systems, laser devices, and much more.
 

     There are two different types of ground Mica, dry ground and wet ground:
 

     Dry ground mica is prepared by grinding it in high speed hammer mills until it is the consistency of flour.  Dry ground mica can be found in joint compound that is used for finishing and filling in seams and blemishes that are found in drywall.  It is a filler and an extender.  It has a smooth consistency and it improves the workability of the compound used.  It has great resistance to cracking.  Joint compound accounts for about 51% of dry ground mica use.
 

    It is also very popular in the paint industry.  It is used as a pigment extender. It helps to facilitate suspension and cuts down on chalking.  It prevents shrinking and shearing of paint film.  It also increases resistance to water penetration and weathering.  Mica also brightens the tone of the pigments.  The use of mica in paint is thought to account for about 24%.
 

    The rubber industry also utilizes mica as an inert filler and mold release compound in the manufacturing of molded rubber products such as tires and roofing supplies.  It makes a very good anti-sticking agent.
 

    Mica is also used by the plastic industry as an extender and filler, especially in the manufacturing of automobile parts such as fascia and fenders. Sometimes it is used as a lightweight insulation to suppress sound and vibration.  It is a reinforcing material that provides improved mechanical properties and increases strength, stiffness, and dimensional stability.
 

    Wet ground mica is often used in industry; it is produced by grinding the mica in water involving preferential delamination of flakes.  Churn mills are used with large wheels or rollers that rotate on horizontal shafts to grind the mica until it is reduced to a fine scale.  Wet ground mica is more costly than dry ground mica. It is used predominantly in paint, rubber, plastics, lubricants, as wallpaper coating and cosmetics.  It is often used wherever its attractive, shiny luster is desired.  It is responsible for the bright, metallic colors on automobiles as well as on a woman’s face.  Its reflective and refractive properties make it an important ingredient in blushes, eye shadows, body and hair glitter, nail polish, and foundation.
 

Where is Mica found?

     Mica is found to occur in thick book forms in pegmatites.  Pegmatites are very coarse grained igneous rocks that have grain size of 20 mm or more.  It is still a subject of research to determine the exact mode of formation of mica, which is found in the form of small flakes to big slabs.  However, it seems to be fairly clear that the degree of presence or absence of orthoclase feldspar indicates the possibility of finding mica within the pegmatite.  It is thought that mica forms at the expense of orthoclase feldspar.
 

    India is the leading producer of muscovite mica, followed by Brazil and Western Africa in Tanzania.

    Leading producers of phlogopite are the Malagasy Republic and Tanzania. Small amounts are also found in Canada and India.

 

References:

Photo References:

http://skywalker.cochise.edu/wellerr/aawellerweb.htm

 

http://images.google.com/imgres?imgurl=http://www.soes.soton.ac.uk/resources/collection/minerals/minerals/images/M31-M-Mica.jpg&imgrefurl=http://www.soes.soton.ac.uk/resources/collection/minerals/minerals/pages/M31-Muscovite.htm&h=467&w=588&sz=79&hl=en&start=104&tbnid=e2BGLdOmoLVNXM:&tbnh=107&tbnw=135&prev=/images%3Fq%3DMica%2Bimages%26start%3D100%26gbv%3D2%26ndsp%3D20%26svnum%3D10%26hl%3Den%26sa%3DN

 

www.mineralminers.com/html/zinmins.stm

 

Text References:

http://www.britannica.com/eb/article-80070/mica

 

http://www.icrmica.com/icrmica_mica_introduction.html

 

http://www.mineralszone.com/minerals/mica.html

 

http://minerals.usgs.gov/minerals/pubs/commodity/mica/440497.pdf

 

http://www.ima-na.org/about_industrial_minerals/mica.asp

 

http://www.mineralminers.com/html/mcaminfo.htm