What are the uses of mica

Mica group

Author: Torsten Purle (steine-und-minerale.de) | Last updated: November 19, 2020


Mica group - properties, formation and use

English: mica | French: mica


Mica and mica

The earliest tradition of the term mica comes from the Year 1546 and goes back to the German mineralogist Georgius Agricola (1494 to 1555). In his work De Natura Fossilium Libri X lists Agricola under the name mica the terms mica and feline silver.
The names mica and mica - the English name for mica - have the same meaning. The term mica is attached to them shiny surface of mica minerals come on; Mica, on the other hand, is taken from Latin and is with sparkle or shine translated.


Properties of mica

The name mica is used in mineralogy not for a single, specific mineral, but for a group of minerals, so-called mica group, which have in common the chemical composition and the crystal lattice structure.
The composition of mica is shown in simplified form as follows: DG2-3[T4O10] X2 With

  • D. = Ammonium (NH4+), Barium, cesium, calcium, potassium, sodium, rubidium
  • G = Aluminum, chromium, iron (Fe2+, Fe3+), Lithium, magnesium, titanium, vanadium, zinc
  • T = Aluminum, beryllium, boron, iron (Fe3+), Silicon
  • X = Anions: Cl, O2−, OH, F, S.2-

According to their composition, mica minerals are assigned to the mineral class of silicates; especially the layered silicates.

Mica crystallizes following the monoclinic, orthorhombic or trigonal crystal system with tabular and pseudo-hexagonal crystals.

Mica is characterized by its perfect cleavability, i.e. the layer-like crystals can be easily broken down into the finest flakes of transparent to translucent transparency and high elasticity. The breakage of mica is flaky.

The Mohs hardness of mica varies between 2 and 4, in some cases some mica have different degrees of hardness in different directions; are generally considered to be very soft minerals on the 10-point scale of the hardness of minerals according to the German mineralogist Carl Friedrich Christian Mohs (1773 to 1839).


The color of mica

Mica are different colors: white, pink, yellowish, brown, silvery-gray, green or violet - always with an intense metallic shimmer.

Sometimes mica is in Light and dark mica differentiated, whereby the color gives an indication of the cations in the respective mica.
⇒ Light mica contains potassium and aluminum, e.g. muscovite
⇒ Dark mica is rich in iron and magnesium, e.g. biotite

The line color of mica - the color that occurs when a mineral is brushed over an unglazed porcelain tablet (streak board) - is white.


Classification of mica minerals

Based on the respective cation and its valence at position D of the general empirical formula of mica, according to the IMA three types of mica differentiated:

  • Real mica: < 50="" %="" einwertige="" kationen="" auf="" der="">
  • Brittle mica: < 50="" %="" zweiwertige="" kationen="" auf="" der="">
  • Interlayer deficient mica:> 0.85 positive charges on the D-digit

SubgroupSub-subgroup line Minerals
Real micaOrdinary potassium micaMuscovite celadonite range
  • Aluminoseladonite
  • Ferro-aluminoseladonite
  • Ferroseladonite
  • Muscovite
  • Celadonite
Phlogopite Annit Series
Siderophyllite-Polylithionite series
  • Polylithionite
  • Siderophyllite
Tainiolite group
Unusual potassium mica
  • Boromuscovite
  • Chromophyllite
  • Eastonite
  • Hendricksite
  • Masutomilith
  • Montdorite
  • Norrishit
  • Roscoelite
  • Tetra Ferri Annite
  • Tetra-ferriphlogopite
  • Trilithionite
Non-potassium micaSodium mica
  • Aspidolite
  • Ephestite
  • Paragonite
  • Price workit
Cesium mica
Ammonium mica
Brittle mica Ordinary brittle mica
  • Clintonite
  • Ferrokinoshitalite
  • Ganterite
  • Cinema hit
  • Margarit
Unusual brittle mica
  • Anandite
  • Bityit
  • Chernykhit
  • Oxykinoshitalite
Interlayer mica
  • Brammallite
  • Glauconite
  • Illite
  • Wonesit


In addition, there are the varieties of the individual minerals such as alurgite, astrolite, fuchsite, gilbertite or sericite as muscovite varieties.


Biotite is a special case

A mineral that is used synonymously with mica in addition to muscovite is biotite.
Indeed it will However, biotite has not been defined as a separate mineral since 1999.

The International Mineralogical Association (IMA), founded in 1958, clarifies whether a mineral corresponds to the definition of a mineral.
In 1998 the Mica Subcommitte was set up to deal with the minerals of the mica group. According to the decision of the international association Biotite is a mixed crystal of the minerals annite and phlogopite; the materially uniform composition of a mineral according to IMA is not given with biotite.
In order to avoid confusion and because biotite has established itself as a term for decades, the name biotite is still accepted.


Mica and feline silver

The term cat silver has been synonymous with mica since the Middle Ages.
Back then, sneaky merchants sold the silvery shimmering mica mineral muscovite as the precious metal silver.
The name addition "cat" stands for the outdated meaning for "deceive or cheat".




Mica minerals as a component of rocks

The minerals of the mica group are contained as aggregates, i.e. mineral components, in various rocks, which are noticeable through the shimmering character in the rock.



Use and meaning of mica

Mica is characterized by a variety of uses.
In the distant past, mica served as a substitute for windows. For this purpose, large crystals were broken up into fine layers, which worked without any problems given the fact that mica was completely cleavable. The individual mica panels were then put together to form a large window and inserted into the window frame. A tradition that has its origins primarily in Russia. The name muscovite gives a first indication of this. Muscovite is translated as "glass from Moscow".

But even today, mica still plays an important role in people's everyday lives.
There are paints and varnishes available in stores to which finely ground mica has been added to create a subtle sheen in the product.

The cosmetics industry also makes use of mica. Mica is used in shimmering eye shadows as well as powders and make-up. Whether a product contains mica can be seen from the declaration of the ingredients (INCI). Mica is listed either under the English word Mica or as CI77019.

Mica is also used for capacitors, insulators and in atomic force microscopy.


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Swell:
⇒ www.minsocam.org - Rieder, M. et al. (1998): NOMENCLATURE OF THE MICAS. IN: The Canadian Mineralogist, Vol. 36, (1998)
⇒ Agricola, G. (1546): De Natura Fossilium Libri X
⇒ Pellant, C. (1994): Stones and Minerals. Ravensburger nature guide. Ravensburger Buchverlag Otto Maier GmbH
⇒ Bauer, J .; Tvrz, F. (1993): The Cosmos Mineral Guide. Minerals rocks precious stones. An identification book with 576 color photos. Gondrom Verlag GmbH Bindlach
⇒ Korbel, P .; Novak, M. and W. Horwath (2002): Mineralien Enzyklopädie, Dörfler Verlag
⇒ Medenbach, O .; Sussieck-Fornefeld, C .; Steinbach, G. (1996): Steinbach's natural guide minerals. 223 species descriptions, 362 color photos, 250 drawings and 30 pages of identification tables. Mosaik Verlag Munich
⇒ Schumann, W. (1991): Minerals rocks - characteristics, occurrence and use. FSVO nature guide. BLV Verlagsgesellschaft mbH Munich

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