Cordierite

• Dichroite
• Iolite
• Water sapphire
• Lynx sapphire

• Mg2Al3 [ AlSi5O18 ]
• (Mg, Fe) 2Al3 [ AlSi5O18 ]

X = c = Light Yellow, Green Y = a = Purple, Blue Violet Z = b = Light Blue

Cordierite, outdated also known as cordierite or Iolite, is a commonly occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the orthorhombic crystal system with the idealized chemical composition Mg2Al3 [ AlSi5O18 ] and thus chemically seen a magnesium aluminum silicate. Structurally cordierite is one of the ring silicates.

Cordierite is the magnesium analogue of Sekaninait ( Fe2Al3 [ AlSi5O18 ] ) and forms a complete solid solution series, hence the mixing formula (Mg, Fe) 2Al3 [ AlSi5O18 ] is for cordierite often quoted, with the elements specified in the parentheses magnesium and iron in the formula each represent each other (substitution, Diadochie ) can, however, always be in the same proportion to the other constituents of the mineral.

In nature cordierite developed rarely well-trained, short to long prismatic crystals. He usually can be found in the form of granular to massive aggregates. It however crystals have been found up to half a meter in length. Uninjured crystal faces have a glass-like luster, fracture surfaces shine on the other hand rather bold similar.

The predominant color of the cordierite is deep blue to blue violet, but rarely it occurs in greenish, yellowish brown, gray or light blue color. Even colorless cordierite are known.

With a Mohs hardness of 7 to 7.5 cordierite is one of the hard minerals, which are as the reference mineral quartz ( 7) in a position to scribe the glass.

Special Features

Cordierite is strongly pleochroic, meaning that visible changes the color of the crystal with the naked eye depending on the light. Since cordierite is birefringent, three different colors, namely bright yellow, violet to blue and light blue show.

Cordierite faceted with chain - view of the colorless b- axis

Etymology and history

The mineral was already Werner Abraham Gottlob (1749-1817) and was known by this name Iolite - from the Greek ἴον [ion ] for violets and λίθος [ lithos ] for stone, so together " violet stone " - due to its schwärzlichblauen, purplish playing color that reminded Werner to a violet.

The French mineralogist Louis Cordier (1777-1861) was the mineral in 1809 the name of cordierite ( " the double -colored "; see Description du dichroite, published 1809). Because the property of the mineral, however, is actually a pleochroism, it was renamed in 1813 by JAH Lucas in cordierite.

Commercially also are following, partly misleading synonyms for the cordierite in circulation:

• Lynx sapphire ( for sapphire with patchy staining)
• Water sapphire ( for colorless topaz )
• Polychroit

As a type locality is considered ground corn or the nearby Great Arber in the Bavarian Forest.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the cordierite belonged to the mineral class of " silicates and Germanates " and then to the Department of " ring silicates ( cyclo- silicates) ," where he, along with Bazzit, beryl, Indialith, Pezzottaite Sekaninait and Stoppaniit was the unnamed group VIII/E.12.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the cordierite in the class of " silicates and Germanates " and then in the Department of the " ring silicates ( cyclo- silicates) ." This division, however, is further divided according to the structure of the rings, so that the mineral according to its construction in the subdivision - is to find " [ Si6O18 ] 12 six- Simple rings without insular complex anions ", where it sold with Sekaninait the " cordierite - group "with the system no. 9.CJ.10 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the cordierite in the class of " silicates and Germanates " and then in the Department of the " ring silicates: Six Rings " field. Here he is with Sekaninait in the " cordierite - group " 61.02.01 within the subdivision of the " ring silicates: Six rings with Al -substituted rings " to find.

Modifications and varieties

The connection Mg2Al3 [ AlSi5O18 ] is dimorphic and is next to the orthorhombic cordierite crystallized as yet crystallized hexagonal high-temperature modification Indialith ago. Due to the strongly inhibited equilibration of dislocations in the crystal lattice, all transitions between Indialith and cordierite are to be found in nature.

As Cerasit is a variety called cordierite, whose habit is similar deen of Trapiche emeralds. Most Cerasite are also converted to muscovite or sericite or pinitol (see muscovite varieties ).

The variety Iolite - Sunstone is a reddish -colored by incorporation of hematite or goethite scales cordierite.

The iron-rich variety Steinheilit got its name from the chemist Johan Gadolin, who named the mineral after its discoverer Fabian Gotthard von Steinheil. This was more interested in mineralogical questions Governor-General of Finland (1810-1812, 1814-1823 ).

Education and Locations

Cordierite is a rock forming mineral and is formed by metamorphism in migmatites, gneisses and pegmatites, but also magmatic in granite. Accompanying minerals occur among others andalusite, biotite, garnet, corundum, muscovite, sillimanite and spinel.

As a rather rare mineral cordierite formation can indeed be abundant in part to different sites, overall it is not very common. Total so far (as of 2014) are around 800 localities for cordierite known. Apart from its type locality Großer Arber in the Bavarian Forest and other locations in the Upper Palatinate in Bavaria, the mineral nor entered into Germany, among others, at several places in the Black Forest as, among others, in the Clara mine in Oberwolfach and a porphyry quarry near Detzeln in Baden- Württemberg, on the Blue dome in Eschwege basin and in the former Marmoritwerk in high places in Hesse, in some places in the surroundings of Bad Harzburg in Lower Saxony, in many places of the North Rhine -Westphalian Seven Mountains near Bad Godesberg and King Winter, in numerous places in the Eifel as under other Andernach and Mendig in Rhineland-Palatinate, at the Schaumberg on ( at Theley ) in Saarland, in several quarries in the vicinity of Chemnitz in Saxony, near Eckernförde in Schleswig-Holstein and the Dolmar at Meiningen in Thuringia.

Known due ausßergewöhnlicher Cordieritfunde is, among other things Näverberg field about 4 km west of the mine of Falun in the Swedish province of Dalarna, where up to 20 cm long, transparent crystals were revealed. The most massive crystals up to 50 cm in length, however, were found at La Fuenfria in the Spanish Sierra de Guadarrama and about half as large crystals that are known from Cerro San Pedro near the Spanish community Guadalix de la Sierra.

In Austria, the mineral among others in a basalt quarry at Pauliberg in Burgenland, in some discovery locations in Carinthia, in Hesse village (community Dunkelsteinerwald ) and at several locations in the Waldviertel in Lower Austria, on Stradner Kogel and in a basalt quarry near Klöch in was Styria, at Kleinstroheim and Kürnberger forest as well as in several places in upper Austria upper Austria and in the shadow tip in Ochsental (Silvretta ) found in Vorarlberg.

In Switzerland, cordierite has so far only in a few places in Bergell (Val Bregaglia ) and Val Rebolgin near Lostallo in the canton of Graubünden and in Brissago in Val Crodolo in Miregn ( Biasca ) and on the Sponda Alp in the community Chironico in Canton Ticino be found.

Other localities lie among others in Algeria, Andorra, Antarctica, Argentina, Ethiopia, Australia, Bolivia, Brazil, China, Finland, France and the French island of Martinique, Georgia, Greenland, India, Iran, Ireland, Israel, Italy, Japan, Kazakhstan, the Democratic Republic of Congo ( Zaire ), Canada, Madagascar, Morocco, Myanmar, Namibia, New Zealand, Norway, Oman, Peru, Poland, Portugal, Romania, Russia, on Saint John ( U.S. Virgin Islands), Slovakia, Sri Lanka, South Africa, Suriname, Tajikistan, Tanzania, Czech Republic, Hungary, the United Kingdom ( UK) and the United States of America (USA).

Crystal structure

Cordierite crystallizes in the orthorhombic space group CCCM ( Raumgruppen-Nr. 66) with the lattice parameters a = 17.09 Å; b = 9.73 Å and c = 9.36 Å and four formula units per unit cell.

Use

The raw materials for technical ceramics, cordierite is mainly produced synthetically. Cordierite foam is a refractory ceramic with low thermal conductivity and expansion. It is used when a high temperature insulation with frequent and large fluctuations in temperature is required ( heat shields, insulation of furnaces, catalytic converters ).

Transparent, light to dark blue minerals are sold as gemstones under the name "Lynx Sapphire " or " water sapphire ".