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Mica



 
 
The mica group of sheet silicate
Silicate

A silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2-, but the silicate species that are encountered most often consist of silicon with oxygen as the ligand...
 (phyllosilicate
Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
) mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s includes several closely related materials having highly perfect basal cleavage.






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Mica in Rock From Alstead
Micasheetusgov
Mica From Alstead
The mica group of sheet silicate
Silicate

A silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. This definition is broad enough to include species such as hexafluorosilicate , [SiF6]2-, but the silicate species that are encountered most often consist of silicon with oxygen as the ligand...
 (phyllosilicate
Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
) mineral
Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s includes several closely related materials having highly perfect basal cleavage. All are monoclinic with a tendency towards pseudo-hexagonal crystal
Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions....
s and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagon
Hexagon

In geometry, a hexagon is a polygon with six edges and six Vertex . A regular hexagon has Schl?fli symbol ....
al sheet-like arrangement of its atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
s.

The word "mica" is thought to be derived from the Latin
Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
 word , meaning "to glitter", in reference to the brilliant appearance of this mineral (especially when in small scales).

Mica classification

Chemically, micas can be given the general formula
X2Y4–6Z8O20(OH,F)4
in which X is K, Na, or Ca or less commonly Ba, Rb, or Cs;
Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc.;
Z is chiefly Si or Al but also may include Fe3+ or Ti.
Structurally the micas can be classed as disoctahedral (Y = 4) and trisoctahedral (Y = 6). If the X ion is K or Na the mica is a common mica whereas if the X ion is Ca the mica is classed as a brittle mica.

Trioctahedral micas

Common micas:
  • Phlogopite
    Phlogopite

    Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of silicate minerals. It is also known as magnesium mica.Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula potassiummagnesium3aluminumsilicon3oxygen102, or 2<...
  • Biotite
    Biotite

    Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
  • Zinnwaldite
    Zinnwaldite

    Zinnwaldite, potassiumlithiumironaluminumoxygen102, is a potassium lithium iron aluminium silicate hydroxide fluoride silicate mineral in the mica group....
  • Lepidolite
    Lepidolite

    Lepidolite It occurs in granite pegmatites, in some high-temperature quartz veins, greisens, and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz, and beryl....
  • Muscovite
    Muscovite

    Muscovite is a Silicate minerals mineral of aluminium and potassium with formula potassiumaluminum22, or 236....
Brittle micas:
  • Clintonite
    Clintonite

    Clintonite is a calcium magnesium aluminium Silicate minerals mineral. It is a member of the margarite group of micas and the subgroup often referred to as the brittle micas....


Interlayer deficient micas

Very fine-grained micas with typically more variation in ion and water content are informally termed clay micas. They include
  • Hydro-muscovite with H3O+ along with K in the X site;
  • Illite
    Illite

    Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a Silicate minerals or layered alumino-silicate. Its structure is constituted by the repetition of Tetrahedron ? Octahedron ? Tetrahedron layer....
     with a K deficiency in the X site and correspondingly more Si in the Z site;
  • Phengite
    Phengite

    Phengite is a series name for dioctahedral micas of composition K224O10, similar to muscovite but with addition of magnesium....
     with Mg or Fe2+ substituting for Al in the Y site and a corresponding increase in Si in the Z site.


Occurrence

The British Geological Survey
British Geological Survey

The British Geological Survey is a partly publicly-funded body which aims to advance geoscience knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research....
 reports that as of 2005, India had the largest deposits of mica in world. China was the top producer of mica with almost a third of the global share, closely followed by the USA, South Korea and Canada. Large Deposits of Sheet Mica were mined in New England from the 19th Century to the 1960s. Large mines existed in Connecticut
Connecticut

Connecticut is a U.S. state located in the New England region of the northeastern United States. The state borders New York to the west and south , Massachusetts to the north, and Rhode Island to the east....
, New Hampshire
New Hampshire

New Hampshire is a U.S. state in the New England region of the Northeastern United States United States of America. The state was named after the southern English Counties of England of Hampshire....
, and Maine
Maine

The State of Maine is a U.S. state in the New England region of the northeastern United States of America, bordering the Atlantic Ocean to the southeast, New Hampshire to the southwest, the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast....
.

Mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatite
Pegmatite

Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic.Most pegmatites are composed of quartz, feldspar and mica; in essence a "granite"....
s.

Until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, its price dramatically dropped when large reserves were found and mined in Africa and South America during the early 1800s. The largest sheet of mica ever mined in the world came from a mine in Denholm, Quebec, Canada.

Scrap and flake mica is produced all over the world. Flake mica comes from several sources: the metamorphic rock called schist
Schist

The schists form a group of Erins metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, Chlorite group, talc, hornblende, graphite, and others....
 as a by-product of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. Sheet mica is considerably less abundant than flake and scrap mica. Sheet mica is occasionally recovered from mining scrap and flake mica. The most important sources of sheet mica are pegmatite deposits.

Properties and uses

Mica has a high dielectric strength
Dielectric strength

In physics, the term dielectric strength has the following meanings:*Of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down, i.e., without experiencing failure of its insulating properties....
 and excellent chemical stability, making it a favoured material for manufacturing capacitors for radio frequency applications. It has also been used as an insulator
Electrical insulation

An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons....
 in high voltage electrical equipment. It is also birefringent
Birefringence

Birefringence, or double refraction, is the decomposition of a Ray of light into two rays when it passes through certain types of material, such as calcite crystals or boron nitride, depending on the polarization of the light....
 and is commonly used to make quarter and half wave plate
Wave plate

A wave plate or retarder is an optics device that alters the polarization state of a light wave travelling through it. A wave plate works by shifting the phase between two perpendicular polarization components of the light wave....
s.

Because mica is resistant to heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
 it is used instead of glass in windows for stove
Stove

A stove is an enclosed heated space. The term is commonly taken to mean an enclosed space in which fuel is burned to provide heating, either to heat the space in which the stove is situated or to heat the stove itself, and items placed on it, for cooking purposes....
s and kerosene heater
Kerosene heater

A kerosene heater, also known as a paraffin heater, is a portable, unvented, kerosene-fueled, space-heating device. In the United States they are used mainly for supplemental heat or as a source of emergency heat during a power outage....
s. It is also used to separate electrical conductors in cable
Cable

A cable is a large fiber or metal rope, used for hauling, lifting, or towing, or an assembly of two or more insulated electrical conductors, laid up together as an assembly....
s that are designed to have a fire-resistance rating
Fire-resistance rating

A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire test. This can be quantified simply as a measure of time, or it may entail a host of other criteria, involving other evidence of functionality or fitness for purpose....
 in order to provide circuit integrity
Circuit integrity

Circuit integrity refers to the operability of electrical circuits during a fire. It is a form of fire-resistance rating. Circuit integrity is achieved via passive fire protection means, which are subject to stringent listing and approval use and compliance....
. The idea is to keep the metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
 conductors from fusing in order to prevent a short-circuit so that the cables remain operational during a fire, which can be important for applications such as emergency lighting.

Illites or clay micas have a low cation exchange capacity
Cation exchange capacity

In soil science, cation exchange capacity is the capacity of a soil for ion exchange of Electric charge ions between the soil and the soil solution....
 for 2:1 clays. K+ ions between layers of mica prevent swelling by blocking water molecules.

Because mica can be pressed into a thin film, it is often used on Geiger-Müller tube
Geiger-Müller tube

A Geiger-M?ller tube is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation, and typically produce an audible click for each....
s to detect low penetrating Alpha particles.

Aventurine
Aventurine

Aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusion s that give a shimmering or glistening effect termed aventurescence....
 is a variety of quartz with mica inclusions used as a gemstone.

Pressed mica sheets are often used in place of glass in greenhouse
Greenhouse

A greenhouse is a building where plants are cultivated.A greenhouse is a structure with a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building....
s.

Mica is often found in mineral cosmetics.

Some brands of toothpaste include powdered white mica. This acts as a mild abrasive to aid polishing of the tooth surface, and also adds a cosmetically-pleasing glittery shimmer to the paste. The shimmer from mica is also used in makeup, as it gives a translucent "glow" to the skin or helps to mask imperfections.

Mica is used in the production of pearlescent pigments.

Many metallic looking pigments are composed of a substrate of mica coated with another mineral, usually TiO2. The resultant pigment produces a reflective color depending on the thickness of the coating. These products are used to produce automobile paint, shimmery plastic containers, high quality inks used in advertsing and security applications.

Mica sheets are used to provide structure for heating wire (such as in Kanthal
Kanthal

Kanthal is an alloy of mainly iron, chromium and aluminium . Kanthal was developed by Hans von Kantzow in Hallstahammar, Sweden. Its name is derived from Kantzow and Hallstahammar....
 or Nichrome
Nichrome

Nichrome is a brand name for a nickel-chromium resistance wire, a non-magnetic alloy of nickel and chromium. A common alloy is 80% nickel and 20% chromium, but there are many others to accommodate various applications....
) in heating element
Heating element

A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters electrical resistance, resulting in heating of the element....
s and can withstand up to .

Another use of mica is in the production of ultraflat thin film surfaces (e.g. gold surfaces) using mica as substrate. Although the deposited film surface is still rough due to deposition kinetics, the back side of the film at mica-film interface provides ultraflatness, when the film is removed from the substrate.

Muscovite
Muscovite

Muscovite is a Silicate minerals mineral of aluminium and potassium with formula potassiumaluminum22, or 236....
 mica is the most common substrate for sample preparation for the atomic force microscope
Atomic force microscope

The atomic force microscope or scanning force microscope is a very high-resolution type of Scanning probe microscopy, with demonstrated resolution of fractions of a nanometer, more than 1000 times better than the diffraction limited....
. Freshly-cleaved mica surfaces have been used as clean imaging substrates in atomic force microscopy, enabling for example the imaging of bismuth
Bismuth

Bismuth is a chemical element that has the symbol Bi and atomic number 83. This heavy, brittle, white crystalline trivalent poor metal has a pink tinge and chemically resembles arsenic and antimony....
 films, plasma glycoprotein
Glycoprotein

Not to be confused with peptidoglycan or proteoglycan.Glycoproteins are proteins that contain oligosaccharide chains covalently attached to their Peptide side-chains....
s, membrane bilayers
Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
, and DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 molecules.

Mica slices
Mica insulator

In the manufacturing of electronic devices, a mica insulator is a die-cut punched Electrical insulation of natural or "block" mica splittings....
 are used in electronics to provide electric insulation between a heat-generating component and the heat sink used to cool it . The same word is sometimes used by technicians to designate a synthetised gum (usually blue or gray) which is used for the same purpose, but which does not actually consist of silicate mineral (language abuse).

Isinglass


Thin transparent sheets of mica called "isinglass" were used for peepholes in boilers and lanterns because they were less likely to shatter compared to glass when exposed to extreme temperature gradients. Such peepholes were also used in "isinglass curtains" in horse-drawn carriages and early 20th century cars. A book about a journey in a Model T Ford car describes isinglass curtains as follows:

"Oiled canvas side curtains were put up over the windows for wind, rain, and cold (there were no heaters) and were held in place with rods that fit into the doors and twisting button snaps around the perimeter... 'Isinglass' peepholes in the curtains allowed limited visibility. Isinglass was made of thin sheets of cracked mica."

Role in primitive life


Helen Hansma, a research scientist affiliated with the University of California, Santa Barbara
University of California, Santa Barbara

The University of California, Santa Barbara, commonly known as UCSB or UC Santa Barbara, is a public university research university and one of the 10 general campuses of the University of California system....
, has proposed that the unique properties of Mica enabled the formation of life in the oceans of the distant past. In atomic force microscopy, biological samples are placed on mica because it is atomically flat. Even bare DNA molecules may be seen as small ridges. Inspecting mica under the microscope, bits of algae and other organic materials suggested to her the possibility early life molecules could have evolved within mica sheets in a communal fashion eons before the evolution of cell membranes or lipid
Lipid

Lipids are broadly defined as any fat-soluble , naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others....
 vesicles
Vesicle (biology)

A vesicle is a small bubble of liquid within a cell. More technically, a vesicle is a small, intracellular, membrane-enclosed sac that stores or transports substances within a cell....
. Mica might have provided a secure place with time and space and protection from the open ocean. Further research might provide additional predictions about energy and entropy for life. Mica is old rock—some earliest evidence for life's most primitive cells is in Akilia Island
Akilia island

Akilia Island is an island in southwestern Greenland, about 22 kilometers south of Nuuk , at . Akilia is the location of a rock formation that has been proposed to contain the oldest known sedimentary rocks on Earth,...
, Greenland
Greenland

Greenland is a member country of the Kingdom of Denmark located between the Arctic Ocean and Atlantic Oceans, east of the Canadian Arctic Archipelago....
, where biotite
Biotite

Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
, a common mica, is also found. Potassium
Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
 ions, which hold the sheets of mica together, are also required by cells. Primordial soup
Abiogenesis

In the natural sciences, abiogenesis, or origin of life, is the study of how life on Earth could have arisen from inanimate matter. It should not be confused with evolution, which is the study of how living things change over time....
  with amino acid
Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
s and simple building blocks of life might have seeped between the water-loving mica sheets. The large planar area between sheets might have facilitated the building of long chain molecules. Negative spaces holding the potassium ions on mica are 0.5 nm apart, as are the single stranded DNA molecules (letters of genetic code), as well as amino acids in proteins. Clay also provides spacing that might encourage this process, but the planar area might better encourage the process. Expansion and contraction caused by temperature changes and ocean currents might provide mechanical energy to help rearrange the molecules and trigger the formation of chemical bonds.

Mica in ancient times

Hand Hopewell Mica
Human use of mica dates back to pre-historic times. Mica was known to ancient Egyptian
Ancient Egypt

Ancient Egypt was an Ancient history civilization in eastern North Africa, concentrated along the lower reaches of the Nile in what is now the modern nation of Egypt....
, Greek
Ancient Greece

The term Ancient Greece refers to the period of History of Greece lasting from the Greek Dark Ages ca. 1100 BC and the Dorian invasion, to 146 BC and the Roman Republic conquest of Greece after the Battle of Corinth ....
 and Roman
Ancient Rome

Ancient Rome was a civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC....
 civilizations, Chinese
History of China

China civilization originated in various city-states along the Yellow River valley in the Neolithic era. The written history of China begins with the Shang Dynasty ....
 civilization, as well as the Aztec
Aztec

Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl and who achieved political and military dominance over large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the Late post-Classic period in Mesoamerican chronology....
 civilization of the New World
New World

The New World is one of the names used for the non-Eurasian/non-African parts of the Earth, specifically the Americas and Australasia. When the term originated in the late 15th century, the Americas were new to the Europeans, who previously thought of the world as consisting only of Europe, Asia, and Africa ....
.

The earliest use of mica has been found in cave paintings created during the Upper Paleolithic
Paleolithic

The Paleolithic or Palaeolithic or "Old Stone" era is a Prehistory era distinguished by the development of the first stone tools, and covers roughly 99% of human history....
 period (40,000 BC to 10,000 BC). The first hues were red (iron oxide
Iron oxide

Iron oxides are chemical compounds composed of iron and oxygen. Altogether, there are sixteen known iron oxides and oxyhydroxides....
, hematite
Hematite

Hematite, Spelling differences#Simplification of ae .28.C3.A6.29 and oe .28.C5.93.29 h?matite, is the mineral form of Iron oxide , one of several iron oxides....
, or red ochre
Ochre

Ochre or Ocher is a color, usually described as Gold -yellow or light yellow brown....
) and black (manganese dioxide, pyrolusite
Pyrolusite

Pyrolusite is a mineral consisting essentially of manganese dioxide and is important as an ore of manganese. It is a soft, black, amorphous appearing mineral, often with a granular, fibrous or columnar structure, sometimes forming reniform crusts....
), though black from juniper or pine carbons has also been discovered. White from kaolin or mica was used occasionally.

A few kilometeres northeast of Mexico City
Mexico City

Mexico City is the capital city of Mexico. It is the most important economic, industrial, and cultural center in the country; the most populous city with over 8,836,045 inhabitants in 2008....
 stands the ancient site of Teotihuacan
Teotihuacán

Teotihuacan is an enormous archaeological site in the Basin of Mexico, containing some of the largest Mesoamerican pyramid built in the pre-Columbian Americas....
. The most striking visual and striking structure of Teotihuacan is the towering pyramid
Pyramid

A pyramid is a building where the outer surfaces are triangular and converge at a point. The base of pyramids are usually quadrilateral or trilateral , meaning that a pyramid usually has four or five faces....
 of the sun. The pyramid contained considerable amounts of locally mined mica in layers up to thick.

Throughout the ages, fine powders of mica have been used for various purposes, including decorative purposes. The colored Gulal and Abeer used by Hindus of north India during holi
Holi

Holi , also called the Festival of Colours, is a popular Hinduism spring festival observed in India, Suriname, Guyana, Trinidad, United Kingdom and Nepal....
 festival contain fine small crystals of mica. The majestic Padmanabhapuram palace
Padmanabhapuram Palace

Padmanabhapuram Palace complex is located in at Padmanabhapuram Fort, close to the town of Thuckalay in Kanyakumari District, Tamilnadu. It is about 20 km from Nagercoil, and about 50 kilometers from Thiruvananthapuram, Kerala....
, from Trivandrum in India, has colored mica windows.

See also

  • Mica insulator
    Mica insulator

    In the manufacturing of electronic devices, a mica insulator is a die-cut punched Electrical insulation of natural or "block" mica splittings....


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