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Fine-needle montmorillonite enclosed in quartz from the "White Queen Mine", Hiriart Mountain, California, USA ( overall size : 12.5 cm × 7.8 cm × 2.7 cm)
General and classification
chemical formula
  • (Na, Ca) 0.3 (Al, Mg) 2 Si 4 O 10 (OH) 2 · nH 2 O
  • (Na, Ca 0.5 ) 0.3 (Al, Mg) 2 [(OH) 2 | Si 4 O 10 ] • 4H 2 O
  • ~ (Al 1.67 Mg 0.33 ) [(OH) 2 | Si 4 O 10 ] • Na 0.33 (H 2 O) 4
Mineral class
(and possibly department)
Silicates and germanates - layered silicates (phyllosilicates)
System no. to Strunz
and to Dana
9.EC.40 ( 8th edition : VIII / H.19)
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 5.18-5.19  Å ; b  = 8.90-8.98 Å; c  = 11.32-12.45 Å
β  = 99.6-100.6 °
Formula units Z  = 2
Physical Properties
Mohs hardness 1 to 2
Density (g / cm 3 ) measured: 2 to 3
Cleavage completely after {001}
Break ; Tenacity uneven
colour white, light pink, yellow-brown to yellow, red, green
Line color White
transparency translucent
shine matt, earthy
Crystal optics
Refractive indices n α  = 1.485 to 1.535
n β  = 1.504 to 1.550
n γ  = 1.505 to 1.550
Birefringence δ = 0.020
Optical character biaxial negative
Axis angle 2V = measured: 5 to 30 °
Pleochroism Visible:
X = colorless to light brown, yellow green
Y = dark brown to yellow green, olive green, light yellow
Z = brown to olive green, light yellow
Other properties
Special features expands many times its original size when water is added

Montmorillonite is a frequently occurring mineral from the mineral class of "silicates and germanates" with the chemical composition (Na, Ca) 0.3 (Al, Mg) 2 Si 4 O 10 (OH) 2 · nH 2 O and therefore chemically one sodium - aluminum - silicate with a variable proportion of water of crystallization . The elements calcium and magnesium in the round brackets can represent each other in the formula ( substitution , diadochie), but are always in the same proportion to the other components of the mineral. Structurally, montmorillonite belongs to the phyllosilicates .

Montmorillonite crystallizes in the monoclinic crystal system , but develops only microscopic, needle-like crystals , which usually form compact, massive aggregates . Also inclusions (inclusions) of montmorillonite in quartz are known. In its pure form, montmorillonite is white. Due to foreign admixtures, montmorillonite can also be yellowish to reddish, greenish or bluish in color. However, the line color is always white.

Montmorillonite is a clay mineral and the most important component (60–80%) of bentonite .

Etymology and history

Montmorillonite was first discovered in the French community of Montmorillon and described in 1847 by Lubin Mauduyt (1782–1870), who named the mineral after its type locality .


Already in the outdated, but still in use 8th edition of the mineral classification according to Strunz , montmorillonite belonged to the mineral class of "silicates and germanates" and there to the department of "phyllosilicates", where it was named after the "montmorillonite group" from three unnamed subgroups with the system no. VIII / H.18 , VIII / H.19 and VIII / H.20 . The mineral montmorillonite is found in subgroup VIII / H.19 together with beidellite , brinrobertsite , nontronite , swinefordite , volkonskoite and yakhontovite .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies montmorillonite in the "layered silicates" department. This is, however, further subdivided according to the structure of the layers, so that the mineral, according to its structure, can be found in the sub-section "Layered silicates (phyllosilicates) with mica tablets, composed of tetrahedral and octahedral networks", where it is also named after the reduced "montmorillonite group" with the system no. 9.EC.40 and the other members beidellite, kurumsakite , nontronite, smectite (mineral group), volkonskoite and yakhontovite.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns montmorillonite to the class of "silicates and germanates" and there in the department of "layered silicate minerals". Here it is together with beidellite, nontronite, volkonskoite and swinefordite in the "smectite group (dioctahedral smectites)" with the system no. 71.03.01a can be found in the subsection “ Layered Silicates: Layers of six-membered rings with 2: 1 clay minerals ”.

Crystal structure

Layered lattice structure of montmorillonite

Montmorillonite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 5.18-5.19  Å ; b  = 8.90-8.98 Å; c  = 11.32–12.45 Å and β = 99.6–100.6 ° and 2 formula units per unit cell . Template: room group / 12

The three-layer structure consists of two tetrahedron layers that are electrostatically crosslinked via the cations of an octahedron intermediate layer . The layers are not rigidly connected to one another, but can swell due to the reversible storage of water and other substances.


Montmorillonite has a high ion exchange capacity , as it can exchange the cations between the layers for those in solution.

When water is added, the mineral expands many times its original size.

Modifications and varieties

A variety containing Fe 3+ is called Mauritzite .

Education and Locations

Tiny, white brushite crystals on gray, coarse montmorillonite (field of view 2 cm)
Montmorillonite and Schörl trapped in quartz from Nuevo, Riverside County, California, USA

Montmorillonite forms hydrothermally through the reaction of minerals and glass components in volcanic tuffs , ashes and bentonites with aqueous solutions. As a clay component , it is found primarily in tropical soils and in the clay mineral fraction of the deep sea soils . Accompanying minerals include various amphiboles and pyroxenes , biotite , calcite , cristobalite , dolomite , gypsum , limonite , various olivines , orthoclase , pyrite , quartz and various zeolites .

As a frequently occurring mineral formation, montmorillonite can be found at many sites, with around 1500 sites worldwide (as of 2017) known to date. In addition to its type locality Montmorillon in the province of Poitou-Charentes , the mineral was also found in France on the Dordogne in Aquitaine , in several places in Auvergne , Brittany and Limousin , near Le Val-d'Ajol in Lorraine, near Espalion in Midi-Pyrénées as well as in several places in the Provence-Alpes-Côte d'Azur region and the former Rhône-Alpes region .

In Germany, montmorillonite is found mainly in Baden-Württemberg , Bavaria , Hesse , Lower Saxony , North Rhine-Westphalia , Rhineland-Palatinate and Saxony , as well as near Barmstedt in Schleswig-Holstein and in Thuringia near 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 municipality of Schlägl .

In Switzerland, montmorillonite has so far been found in Le Locle (Neuchâtel), Waldkirch (St. Gallen), Bischofszell (Thurgau), in the Binntal (Valais) as well as in Wiesendangen and Zurich .

Other 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 , Czech Republic , Turkey , Turkmenistan , Ukraine , Hungary , Uzbekistan , the United Kingdom (Great Britain), the United States of America (USA), Vietnam and Belarus .

Montmorillonite was also found in rock samples from Mars , more precisely from Mawrth Vallis .


The swelling behavior of the crystals in the presence of water opens up a wide range of applications for the mineral. In aqueous drilling fluids , it increases the viscosity , which improves the cooling of the drill bit and aids in the removal of the rock material from the borehole.

In oil production , montmorillonite plays a certain role as a water-blocking agent in order to prevent toxic substances from rising up into higher layers in old boreholes.

As an additive in soil and rocks, montmorillonite slows down the seepage of water (for example in agriculture to bridge longer dry periods).

In plastics it is used (besides many other substances) as a filler material or additive to change the properties of the polymer ( e.g. in nanocomposites ).

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

The montmorillonite bentonite flour is used as a mineral additive for ponds and aquariums under various product names.

In the medical and veterinary field, montmorillonite is used as an ingredient in antidiarrhoeic drugs . It is used in foundries as an inorganic binding agent for sands. In addition, montmorillonite is used as a desiccant and prevents the formation of condensation in transport packaging in fleece bags of different sizes.


  • L. Mauduyt: Un mot sur un morceau de quartz d'une variété particulière, ainsi que sur une substance minérale trouvée dans le département de la Vienne . In: Bulletin de la Société Géologique de France . tape 4 , 1847, p. 168–170 ( [PDF; 230 kB ; accessed on March 19, 2017]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 752–753 (first edition: 1891).
  • Helmut Schrätze , Karl-Ludwig Weiner : Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 826-828 .
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 567-572 .

Web links

Commons : Montmorillonite  - collection of images, videos and audio files

Individual evidence

  1. a b IMA / CNMNC List of Mineral Names; January 2017 (English, PDF; 1.66 MB)
  2. a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  3. ^ Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  670 .
  4. Webmineral - Montmorillonite (English)
  5. a b c American-Mineralogist-Crystal-Structure-Database - Montmorillonite (English)
  6. a b Dimitrios Gournis, Alexandros Lappas, MA Karakassides, Daniel M. Többens, A. Moukarika: A neutron diffraction study of alkali cation migration in montmorillonites . In: Physics and Chemistry of Minerals . tape 35 , 2008, p. 49-58 , doi : 10.1007 / s00269-007-0197-z .
  7. a b c d Montmorillonite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( [PDF; 83  kB ]).
  8. a b c d e f Mindat - Montmorillonite (English)
  9. Laetitia Rouleau: Mythique montmorillonite . In: L'Actualité poitou-charentes . April 2011 ( [PDF]).
  10. Mindat - Number of localities for Montmorillonite
  11. a b List of localities for montmorillonite in the Mineralienatlas and in Mindat - Localities for Montmorillonite
  12. Data sheet Diarsanyl Plus at Vetpharm