Vermiculite

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Vermiculite
Vermiculite-362652.jpg
Mica-like, tabular vermiculite from Paakkila, Tuusniemi , Eastern Finland (field of view approx. 1.5 cm × 1.5 cm)
General and classification
chemical formula
  • Mg 0.7 (Mg, Fe, Al) 6 (Si, Al) 8 O 20 (OH) 4 · 8H 2 O
  • (Mg 0.5 , Ca 0.5 , Na, K) 0.7 (Mg, Fe, Al) 3 [(OH) 2 | (Al, Si) 2 Si 2 O 10 ] · 4H 2 O
Mineral class
(and possibly department) 		Silicates and germanates - layered silicates (phyllosilicates)
System no. to Strunz
and to Dana 		9.EC.50 ( 8th edition : VIII / H.21)
71.02.02d.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m (according to Schoenflies : C 2h )
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 5.35  Å ; b  = 9.26 Å; c  = 28.89 Å
β  = 97.1 °
Formula units Z  = 4
Physical Properties
Mohs hardness 1.5 to 2
Density (g / cm 3 ) measured: 2.2 to 2.6; calculated: 2.26
Cleavage completely after {001}
Break ; Tenacity uneven
colour colorless, gray-white, yellow-brown, gray-green, green
Line color greenish-white
transparency translucent to opaque
shine Greasy, sometimes earthy
Crystal optics
Refractive indices n α  = 1.525 to 1.561
n β  = 1.545 to 1.581
n γ  = 1.545 to 1.581
Birefringence δ = 0.020
Optical character biaxial negative
Pleochroism colorless-yellow-green to brown-green-yellow-green to brown-green

The mineral vermiculite is a rather rarely occurring layered silicate from the mineral class of "silicates and germanates" with the general chemical composition (Mg 0.5 , Ca 0.5 , Na, K) 0.7 (Mg, Fe, Al) 3 [ (OH) 2 | (Al, Si) 2 Si 2 O 10 ] · 4H 2 O or somewhat simplified Mg 0.7 (Mg, Fe, Al) 6 (Si, Al) 8 O 20 (OH) 4 · 8H 2 O. The elements given in brackets can represent each other, but are always in the same proportion to the other components of the mineral ( substitution ).

Vermiculite crystallizes in the monoclinic crystal system and develops exclusively leafy, scaly or massive aggregates that are either colorless or gray-white, yellow-brown, gray-green or green due to foreign admixtures.

Vermiculite is one of the clay minerals that contribute significantly to soil fertility due to its ion exchange capacity. Both structurally and in terms of their appearance, they are similar to the mica minerals and, like them, form flaky crystals .

Etymology and history

Vermiculite was first discovered near Millbury in Worcester County in the US state of Massachusetts and described in 1824 by Thomas H. Webb. Due to the property of the mineral to expand into worm-shaped structures when heated to 200 to 300 ° C in the direction of the crystallographic c-axis, Webb named it after the Latin word vermiculor for "worm breeder" (also vermis for "worm" or vermiculus for " Worms "). On the occasion of the 195th anniversary of its discovery and due to its great importance as an industrial mineral, vermiculite was voted "Mineral of the Year" in Austria in 2019.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , vermiculite belonged to the mineral class of "silicates and germanates" and to the department of "phyllosilicates", where it belongs to the large family of "clay minerals" , but nevertheless formed the independent group VIII / H.21 for itself .

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 assigns vermiculite to the class of "silicates and germanates" and there in the department of "phyllosilicates". This division is, however, further subdivided according to the internal structure of the layers, so that the mineral, according to its structure, can be found in the sub-division of "phyllosilicates (phyllosilicates) with mica tablets, composed of tetrahedral or octahedral nets", where it can be found together with tibiscumite, the unnamed Forms group 9.EC.50 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns vermiculite to the class of "silicates and Germanates" and there in the section of "layered silicate minerals". Here it is together with hydrobiotite, illite and brammallite in the "mica group (hydro mica subgroup)" with system no. 71.02.02d can be found in the subsection “ Layered Silicates: Layers of six-membered rings with 2: 1 layers ”.

Crystal structure

Vermiculite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 5.35  Å ; b  = 9.26 Å; c  = 28.89 Å and β = 97.1 ° and 4 formula units per unit cell . Template: room group / 15

Structurally , vermiculite can be described as a di- and trioctahedral 2: 1 layer of silicate :

In each case two layers of tetrahedrally coordinated cations form such a 2: 1 silicate layer with a layer of octahedrally coordinated cations in between. In trioctahedral vermiculites, mainly magnesium ions are found in the octahedral position , which ensure that the octahedral coordinated cation sites are almost completely occupied. The tetrahedron layer has a Si 4+ : Al 3+ ratio of 1: 2 to 1: 3. This isomorphic replacement in the tetrahedral layers (Al 3+ for Si 4+ ) results in a negative excess charge of the silicate layer, which can be reduced by isomorphic replacement in the octahedral layers (e.g. Fe 3+ for Mg 2+ ).

In total, vermiculites have a negative excess charge of 1.2 to 1.8 elementary charges per unit cell . This negative excess charge is balanced out by hydrated cations in the intermediate layer. Depending on the type of interlayer ion and the chemical composition of the 2: 1 silicate layer and depending on the water vapor partial pressure and the temperature of the atmosphere surrounding the mineral, there are different amounts of water in the interlayer of the vermiculite.

The amount of water and the corresponding base plane distance d 001 do not vary continuously depending on the water vapor partial pressure and temperature, but rather discrete hydration states with sharp transitions between these states can be observed. With increasing temperature or decreasing water vapor partial pressure, the vermiculites gradually change into hydration states with less and less interlayer water and thus smaller d 001 base plane distances.

Modifications and varieties

As batavite a low iron content is variety of vermiculite referred.

Education and Locations

The most important vermiculite deposits are mainly formed hydrothermally or by weathering of phlogopite / biotite , chlorite and pyroxene in basic to ultra-basic rocks. Natural dioctahedral vermiculites have not yet been found except in the clay fraction of soils, from which they cannot, however, be separated purely.

As a rather rare mineral formation, vermiculite can sometimes be abundant at various sites, but overall it is not very common. Currently (as of 2014) around 550 sites are known. In addition to its type locality Millbury and the nearby Ballard quarry near Worcester , the mineral occurred in Massachusetts at Tyringham in Berkshire County , in the Davis pyrite mine near Rowe in Franklin County and the asbestos mine near Pelham in Hampshire County .

Other locations include Australia, Brazil, China, Germany, France, Canada, Madagascar, Austria, Russia, Switzerland, South Africa and other states of the USA.

use

Vermiculite is used industrially in cat litter and for the production of carnival articles (fireworks). Since, unlike asbestos , it is not carcinogenic, it is also used for sound and heat insulation and fire protection. Half of the annual production comes from South Africa.

Vermiculite is also used in the vegetable industry as a cover material for seedlings after sowing. It is light and has the ability to reflect light and retain moisture. This prevents the seedlings from overheating and ensures a more balanced substrate moisture content.

Vermiculite is also often used in reptile breeding and keeping, where the constant humidity in the terrarium, wet boxes and incubator is vital for the animals, because it absorbs excess moisture, including from the air, and releases it again when necessary .

Due to its low thermal conductivity (λ = 0.06 ... 0.07 W / (m · K)), vermiculite is used as a thermal insulation board or non-combustible board material (A1 or A2 according to DIN 4102) in ship interiors and also in building construction. This product is offered worldwide under the brand names “Fipro”, “Miprotec”, “bro-TECT”, “Vermilite 2000” and “Thermax”.

Since vermiculite has a high melting point (1315 ° C), is electrically non-conductive and there is no stratification when freezing, it is used as the core material in infrared heating.

In combination with iron powder, water, cellulose (or polypropylene), salt and activated charcoal, vermiculite is used to make hand warmers . When the hand warmer is unpacked (i.e. when air gets into the package), an extremely fast oxidation process (in this case the iron rusting) is triggered. The salt acts as a catalyst and the activated carbon helps to distribute the heat evenly in the hand warmer. Vermiculite acts as an insulator and cellulose (or PP) helps distribute the air between the components if the hand warmers are used in a humid environment. The resulting temperatures reach up to 75 ° C (approx. 180 ° F). The heat is retained for one to twenty hours, depending on the outside temperature. However, these types of hand warmers are not reusable. They are disposed of with normal household waste because they are not harmful to the environment.

Vermiculite is pretreated by dry heating for use in various areas where absorbency and good thermal insulation are important. At temperatures between 700 and 1000 ° C, the water of crystallization it contains evaporates and pushes the crystal flakes apart. The volume and the absorbency increase significantly while the bulk density decreases. This material is known in the industry as expanded vermiculite .

Since vermiculite - even after expansion - is non-flammable, but absorbent to a certain extent, it is often used for packaging hazardous liquid goods . For example, hazardous substances filled in glass bottles are packed in cardboard boxes or tin cans and the space between the glass and the outer packaging is completely filled with vermiculite. In this way, on the one hand, any leaking chemicals are absorbed, on the other hand, glass breakage is avoided in advance, as the surrounding vermiculite layer also provides good protection against mechanical impacts against the packaging. Waste collectors also like to use vermiculite as a filler for the safe collection and storage of lithium-ion batteries .

Vermiculite and cement can be used to produce concrete with good thermal insulation and temperature resistance ( vermiculite concrete ).

See also

literature

  • Thomas H. Webb: New localities of tourmalines and talc . In: American Journal of Science and Arts . tape 7 , 1824, p. 55–55 (English, rruff.info [PDF; 149 kB ; accessed on June 14, 2019]).
  • Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 108 .
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 255 .

Web links

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

Individual evidence

  1. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: March 2019. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, March 2019, accessed May 20, 2019 .
  2. ^ A b David Barthelmy: Vermiculite Mineral Data. In: webmineral.com. Retrieved June 14, 2019 .
  3. ^ A b c 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.  672 (English).
  4. ↑ a b Vermiculite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 81  kB ; accessed on June 14, 2018]).
  5. ↑ a b c d Vermiculite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 14, 2019 .
  6. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  7. ^ Thomas H. Webb: New localities of tourmalines and talc . In: American Journal of Science and Arts . tape 7 , 1824, p. 55–55 (English, [1] [PDF; 149 kB ; accessed on June 14, 2019]).
  8. ^ Karl Hartmann: Description and decomposition of several new minerals. 37) vermiculite . In: Otto Linné Erdmann, Franz Wilhelm Schweigger-Seidel (Hrsg.): Journal for practical chemistry . tape 8 . Publisher by Johann Ambrosius Barth, Leipzig 1836, p. 505 ( limited preview in Google Book Search [accessed June 14, 2019]).
  9. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 339 .
  10. ↑ Mineral of the year in Austria. In: www.mineraldesjahres.at. Retrieved October 3, 2019 .
  11. ↑ Localities for vermiculite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 14, 2019 .
  12. ↑ locality list for vermiculite in Mineralienatlas and Mindat
  13. ↑ Vermiculite / vermiculite. In: www.klein-daemmstoffe.de. Small insulation materials, accessed on June 14, 2019 .
  14. ↑ Product description Vermiculite. In: vermiculite.de. Isola Vermiculite, accessed June 14, 2019 .
  15. ↑ (Richard Feischl, Albert Brix, Franz Schneeflock, Markus Fellner, Alexander Dippelreiter): Leaflet on fire protection requirements for the storage of lithium ion batteries in waste material collection centers. (PDF) In: www.noe122.at. Lower Austrian Fire Brigade Association, accessed on June 14, 2019 .
  16. ↑ Armin Petzold, Manfred Röhrs: Concrete for high temperatures . Beton-Verlag, Düsseldorf 1965, DNB  453751849 , p. 173 .