Montmorillonite

The mineral montmorillonite is a common layer silicate having the chemical composition ~ ( AL1, 67Mg0, 33) [( OH) 2 | Si4O10 ] • NA0, 33 (H2O ) 4 It crystallizes in the monoclinic crystal system and developed only microscopic, needle-shaped crystals, which usually form compact, massive aggregates. Also inclusions ( inclusions) of montmorillonite in quartz are known.

In pure form, montmorillonite is white. Through foreign admixtures montmorillonite but can also be colored yellowish to reddish, greenish or bluish. The stroke color is, however, always white.

Montmorillonite is a clay mineral and most substantial part (60-80 %) of bentonite.

Special Features

Montmorillonite has a high ion exchange capacity, as it is able to exchange the cations between the layers against the in solution.

Upon addition of water, the mineral expands to many times its original size.

Etymology and history

Montmorillonite was first discovered in the French community Montmorillon and described in 1847 by Mauduyt, who named the mineral after its type locality.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the montmorillonite belonged to the mineral class of " silicates and Germanates " and then to the Department of " layer silicates ( phyllosilicates ) ," where he along with the smectites namesake of the member achieve " smectite / montmorillonite group " was.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of Strunz 's Mineral classification assigns the montmorillonite also included in the category of " silicates and Germanates " and there in the department of " layer silicates ( phyllosilicates ) ". This division, however, is further subdivided according to the crystal structure, so that the mineral according to its construction in the subdivision of " layer silicates ( phyllosilicates ) with mica sheets, composed of tetrahedral and octahedral nets " can be found where there is a namesake of the " montmorillonite " with the System no. Forms 9.EC.40 and the other members beidellite, Kurumsakit, nontronite, volkonskoite and Yakhontovit.

The classification of minerals according to Dana assigns the montmorillonite in the class of " silicates and Germanates " and there in the department of " layer silicate minerals " one. Here he is with beidellite, nontronite, volkonskoite and Swinefordite in the " smectite ( dioctahedral smectites ) " with the system no. To find " layers of six-membered rings with 2:1 phyllosilicates clay minerals " 71.03.01a within the subdivision.

Modifications and varieties

A Fe3 - containing variety is called Mauritzit.

Education and Locations

Montmorillonite is hydrothermally formed by substitution of other minerals in volcanic tuffs, ash and bentonite. As a clay component it is mainly found in tropical soils and the clay mineral of the ocean floors. Accompanying minerals are amphiboles and pyroxenes, among others, various, biotite, calcite, cristobalite, dolomite, gypsum, limonite, various olivine, orthoclase, pyrite, quartz, and various zeolites.

Worldwide, montmorillonite far (as of 2011) are detected at around 1100 localities. Apart from its type locality Montmorillon in the province of Poitou -Charentes in France, the mineral was still Dorgogne in Aquitaine, in several places in the Auvergne, Brittany and Limousin, near Le Val- D'Ajol in Lorraine, at Espalion in Midi-Pyrenees, as well as several places of Provence -Alpes- Côte d' Azur and Rhône -Alpes.

In Germany, montmorillonite found mainly in Baden- Württemberg, Bavaria, Hesse, Lower Saxony, North Rhine -Westphalia, Rhineland -Palatinate and Saxony, and in Barmstedt in Schleswig-Holstein and Thuringia in Gera and Meiningen.

In Austria, the mineral could be found in several places in Burgenland, Carinthia, Salzburg and Styria as well as in the Upper Austrian town Schlaegl.

In Switzerland, montmorillonite was previously in Le Locle (Neuchâtel), Waldkirch SG (St. Gallen), Bischofszell ( Thurgau ), in the Binn Valley (Valais ) and in Wiesendangen and Zurich.

More Locations are Afghanistan, Argentina, Armenia, Australia, Brazil, Bulgaria, Chile, China, Denmark, Ecuador, Fiji, Finland, Georgia, Greece, Greenland, Guam, India, Indonesia, Iran, Ireland, Israel, Italy, Japan, Cambodia, Cameroon, Canada, Kazakhstan, Kyrgyzstan, Democratic Republic of the Congo, North and South Korea, Kosovo, Madagascar, Morocco, Mexico, Mongolia, Mozambique, Namibia, Netherlands, New Zealand, Norway, Oman, Pakistan, Papua New Guinea, Peru, Philippines, Poland, Portugal, Romania, Russia, Sweden, Senegal, Serbia, Zimbabwe, Slovakia, Slovenia, Spain, South Africa, Taiwan, Turkey, Turkmenistan, Ukraine, Uzbekistan, the United Kingdom ( UK), the United States of America ( USA), Vietnam and Belarus.

Even in rock samples from Mars, or more precisely from Mawrth Vallis montmorillonite was detected.

Crystal structure

Montmorillonite crystallizes in the monoclinic space group ( Raumgruppen-Nr. 12) with the lattice parameters a = 5.17 Å; b = 8.94 Å; c = 15.24 Å and β = 94 ° and two formula units per unit cell.

The three-layer structure consisting of two tetrahedral layers are crosslinked electrostatically on an octahedral cations interlayer. The layers are not rigidly connected to each other, but can swell by reversible intercalation of water and other substances.

Use

The swelling behavior of the crystals in the presence of water opens up versatile applications for the mineral. In aqueous drilling muds, it increases the viscosity, which improves the cooling of the drill bit support and the removal of the rock material from the wellbore.

In oil production montmorillonite plays as a water - blocking agent a certain role to prevent in old wells the rise of toxic substances in higher layers.

In addition, in soils and rocks montmorillonite slows the seepage of water ( for example, in agriculture to bridge prolonged dry periods ).

In plastics it is ( besides many other substances ) was used as filler or additive for altering the characteristics of the polymer (eg in nanocomposites ).

It is sold under the name Lavaerde finely ground as a shampoo.

Among various product names the montmorillonite bentonite powder is used as a mineral addition for pond and aquarium use.

It is also used in the medical and veterinary medicine as an ingredient for antidiarrheals.

In addition, montmorillonite found in foundries using as an inorganic binder of sands.