Faujasite

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Faujasite
Faujasite subgroup-466643.jpg
Octahedral faujasite crystals (edge ​​lengths ≈ ¾ mm) as drusen filling from the Limberg quarry, Sasbach am Kaiserstuhl , Baden-Württemberg
General and classification
chemical formula (Na, Ca 0.5 , Mg 0.5 , K) x (Al x Si 12-x O 24 ) • 16H 2 O
Mineral class
(and possibly department) 		Silicates and Germanates - framework silicates
System no. to Strunz
and to Dana 		9.GD.30 ( 8th edition : VIII / J.27)
77.01.02.07 to 77.01.02.07b
Similar minerals Chabazite , Gmelinite , Lévyn , Erionite etc. a. Zeolites
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fd 3 m (No. 227)Template: room group / 227
Lattice parameters see crystal structure
Formula units Z  = 16
Twinning after {111} contact and penetration twins
Physical Properties
Mohs hardness 4.5 to 5
Density (g / cm 3 ) 1.92 to 1.93
Cleavage completely after {111}
Break ; Tenacity uneven to shell-like; brittle
colour colorless, white, yellowish, brownish
Line color White
transparency transparent to translucent
shine Glass gloss to diamond gloss
Crystal optics
Refractive index n  = 1.466 to 1.480
Birefringence none, as it is optically isotropic

Faujasite is the collective name for an unspecified mineral of a mixed crystal series with the end members faujasite-Ca , faujasite-Mg and faujasite-Na from the mineral class of "silicates and germanates" recognized by the International Mineralogical Association (IMA) . Structurally, the Chabazites belong to the framework silicates (tectosilicates) and there to the family of zeolites .

All members of the Chabazite series crystallize in the cubic crystal system with the general chemical composition (Na, Ca 0.5 , Mg 0.5 , K) x (Al x Si 12-x O 24 ) · 16H 2 O, with the addition of the name denotes the predominant cation ( -Na for sodium , -Ca for calcium , -Mg for magnesium ). The value of x in the above formula usually varies between 3.2 and 3.8. By substitution it can also contain potassium and some strontium .

Faujasite only develops small, mostly octahedral and rarely trisoctahedral crystals of a few millimeters in size with a glass-like to diamond-like shine on the surfaces. In pure form, faujasite crystals are colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline design, they can also appear white and take on a yellowish or brownish color due to foreign admixtures, whereby the transparency decreases accordingly.

With a Mohs hardness of 4.5 to 5, faujasite is one of the medium-hard minerals that, like the reference mineral apatite (5), can just be scratched with a pocket knife .

Industrially synthesized faujasites include designation zeolite X and zeolite Y known.

Etymology and history

Barthélemy Faujas de Saint-Fond (1741–1819)

Faujasite was first described in 1842 by Augustin Alexis Damour by Sasbach am Kaiserstuhl in Baden-Württemberg and was named in honor of the French geologist and volcanologist Barthélemy Faujas de Saint-Fond . The structure of faujasite was first reported in 1956.

In the course of the revision of the zeolite nomenclature in 1997 by the IMA, the end links of the faujasite mixed series were also redefined. The quarries near Sasbach are still the type locality for faujasite-Na and the hypothetical mineral faujasite-Mg, which is defined as an additional end link. A drill core from Haselborn near Ilbeshausen am Vogelsberg is given for faujasite-Ca .

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the faujasites belonged to the mineral class of "silicates and germanates" and there to the department of "tectosilicates (tectosilicates), with zeolites", where they together with analcime , paulingite- Ca , Paulingit-K , Pollucit and Wairakit within the zeolite group the subgroup of the "Cube Zeolites II" with the system no. VIII / J.27 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also assigns the faujasites to the category of “framework silicates (tectosilicates) with zeolitic H 2 O; Family of zeolites ”. However, this is further subdivided according to the structure of the framework, so that the minerals can be found according to their composition in the sub-section “Chains of five rings”, where they form the unnamed group 9.GD.30 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the faujasites to the class of "silicates and Germanates" and there in the department of "framework silicates: zeolite group". Here they are in the " Chabazite and allied species " with the system no. 77.01.02 to be found in the subsection "Real Zeolites".

Crystal structure

Sodalite cage
Structure of faujasite

All faujasites crystallize cubically in the space group Fd 3 m (space group no.227) with the following lattice parameters with 16 formula units per unit cell : Template: room group / 227

For faujasite-Mg as a hypothetical terminal link, no independent structural data exist so far.

The crystal structure of faujasite is identical to that of synthetic zeolite Y. The basic element of the faujasite framework are sodalite cages , which are connected to one another via hexagonal prisms. The pores are arranged perpendicular to one another. The pore formed by a ring of 12 units is relatively large, 7.4 Å in diameter. The interior has a diameter of 12 Å and is surrounded by 10 sodalite cages. The unit cell is cubic with a length of 24.7 Å. Faujasite materials are characterized by a large surface and a narrow pore distribution in the range from 0.9 to 1.2 nm, as well as by a high thermal resistance.

Education and Locations

Faujasite Na from the Poudrette Quarry, Mont Saint-Hilaire , Québec, Canada (field of view 2.0 mm × 2.0 mm)
Faujasite octahedron (edge ​​lengths ≈ ½ mm) with "cracked" surfaces from the Limberg quarry, Sasbach am Kaiserstuhl , Baden-Württemberg

Like many other zeolites, faujasite is a typical product of the hydrothermal transformation of basaltic volcanic rocks . After the eruption , the rock is gradually altered by the circulation of hot solutions . The entrained solution load precipitates in drusen and on crevices . At the classical site of the Kaiserstuhl faujasite grows in free-standing crystals in cavities in Druze limburgite - lava flows . In addition to other zeolites, augite , olivine and nepheline can also occur as accompanying minerals .

Faujasites are among the rare mineral formations and could therefore only be detected at a few sites, whereby so far (as of 2014) around 40 sites are known. However, since these finds are rarely analyzed with sufficient precision, information on the individual English songs with regard to the number of sites is correspondingly inaccurate.

In addition to its original type locality Sasbach am Kaiserstuhl in Baden-Württemberg, the mineral has so far been found in various quarries near Alten-Buseck , Annerod , Grossen-Buseck , Wehrda (Marburg) , Langd and Ilbeshausen in Hesse; on the Rother Kopf near Roth ( Gerolstein ) and on the Graulay (Graulai, Graulei, Grauley) near Hillesheim (Eifel) in Rhineland-Palatinate and near Eisenach in Thuringia.

Other locations are in Italy, Jordan, Canada, Spain, the Czech Republic and the United States of America (USA).

use

In contrast to its synthetic counterpart, zeolite Y , which is industrially produced in large quantities, natural faujasite has no practical significance due to its rarity.

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e Douglas S. Coombs, Alberto Alberti, Thomas Armbruster, Gilberto Artioli, Carmine Colella, Ermanno Galli, Joel D. Grice, Friedrich Liebau, Joseph A. Mandarino, Hideo Minato, Ernest Henry Nickel , Elio Passasslia, Donald R. Peacor, Simona Quartieri, Romano Rinaldi, Malcom Ross, Richard A. Sheppard, Ekkehart Tillmanns, Giovanna Vezzalini: Recommended nomenclature for zeolite minerals: report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names. In: The Canadian Mineralogist. Volume 35 (1997), pp. 1571–1606 ( PDF 3.3 MB ; faujasite series from p. 11)
  2. ↑ a b c American-Mineralogist-Crystal-Structure-Database - Faujasite
  3. ^ M. Damour: Description de la faujasite, nouvelle espèce minérale. In: Annales des Mines. Volume 4.1 (1842), pp. 395-399.
  4. ↑ G. Bergerhoff, WH Baur, W. Nowacki: About the crystal structure of the Faujassites. In: New yearbook for mineralogy, monthly books. 1958, pp. 193-200
  5. ^ D. Karami, S. Rohani: Synthesis of pure zeolite Y using soluble silicate, a two-level factorial experimental design. In: Chemical Engineering and Processing. Volume 28 (2009), pp. 1288-1292 doi : 10.1016 / j.cep.2009.05.007
  6. ↑ Mindat - Number of localities for Faujasite
  7. ↑ List of localities for faujasites in the Mineralienatlas and Mindat