Scolecite
| Scolecite | |
|---|---|
 |
|
| General and classification | |
| other names |
Calcareous mesotype |
| chemical formula | Ca [Al 2 Si 3 O 10 ] • 3H 2 O |
|
Mineral class (and possibly department) |
Silicates and Germanates - framework silicates (tectosilicates) |
|
System no. to Strunz and to Dana |
9.GA.05 ( 8th edition : VIII / J.21) 77.01.05.05 |
| Similar minerals | Natrolite , mesolite |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic; m |
| Space group | Cc (No. 9) |
| Lattice parameters |
a = 18.51 Å ; b = 18.97 Å; c = 6.53 Å β = 90.6 ° |
| Formula units | Z = 8 |
| Frequent crystal faces | {010}, {110}, {111} |
| Twinning | according to [001] pseudorhombic contact and penetration twins with stripes according to {010} |
| Physical Properties | |
| Mohs hardness | 5 to 5.5 |
| Density (g / cm 3 ) | measured: 2.25 to 2.29; calculated: 2.275 |
| Cleavage | completely according to {110} and {1 1 0} |
| Break ; Tenacity | uneven; brittle |
| colour | colorless, white |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass gloss, silk gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.507 to 1.513 n β = 1.516 to 1.520 n γ = 1.517 to 1.521 |
| Birefringence | δ = 0.010 |
| Optical character | biaxial negative |
| Axis angle | 2V = 36 to 56 ° (measured); 36 to 40 ° (calculated) |
| Other properties | |
| Special features | pyroelectric, piezoelectric, occasionally fluorescence |
Skolezite , also known as the lime mesotype , is a rather seldom occurring mineral from the mineral class of " silicates and germanates " with the composition Ca [Al 2 Si 3 O 10 ] · 3H 2 O and is therefore a calcium - aluminum silicate. Due to its crystal structure, Skolezit is one of the tectosilicates and there to the group of fiber zeolites .
Scolecite crystallizes in the monoclinic crystal system and develops predominantly long, prismatic to needle-like crystals in radial mineral aggregates . Fibrous, spherical and bulky aggregates as well as contact and penetration twins are known. The crystals are transparent to translucent and undamaged crystal surfaces have a glass-like sheen . Fine-needle aggregates, on the other hand, tend to have a silky sheen.
Together with natrolite (Na 2 [Al 2 Si 3 O 10 ] · 2H 2 O), skolezite forms a seamless series of mixed crystals , which is characterized by the exchange of sodium instead of calcium and the release of part of the water of crystallization . Mesolite is the intermediate link.
Etymology and history
The name of the mineral refers to the worm-like curving of scolezite when heated before the soldering tube ( Greek skolex , worm).
Skolezite was first described in 1813 by the German scholars Adolph Ferdinand Gehlen and Johann Nepomuk Fuchs . Whether the material they investigated, as later assumed, actually comes from the Berufjörður area in Iceland (which is commonly regarded as a type locality ), however, is not guaranteed.
The term mesotype, originally coined by René-Just Haüy in 1801 (from the Greek μέσος for center and τύπος for shape) was used until the 20th century for the minerals natrolite ( soda mesotype ), mesolite and scolezite ( lime mesotype ) known and summarized today as the natrolite group .
classification
In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz was one of the mineral class of "silicates and Germanates" and then to the Department of " framework silicates (tectosilicates)" where he collaborated with Gonnardite , Mesolith, natrolite, Paranatrolith , Thomsonit - (Ca) and thomsonite (Sr) the " zeolite group : subgroup fiber zeolites" with the system no. VIII / J.21 formed.
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 the scolezite to the class of "silicates and germanates", but there in the more finely subdivided section of "tectosilicates" with zeolitic H 2 O; Family of zeolites ”. This section is further subdivided according to the crystal structure, so that the mineral can be found in the sub-section “Zeolites with four-ring chains connected via a fifth Si” according to its structure, where together with gonnardite, mesolite, natrolite and paranatrolite the “ Natrolithgruppe “with the system no. 9.GA.05 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the scolezite to the class of "silicates and Germanates" and there in the department of "framework silicates: zeolite group". Here it is together with natrolite, tetranatrolite , paranatrolite, mesolite, edingtonite , gonnardite, cowlesite , thomsonite (Ca), thomsonite (Sr) and nabesite in the group "natrolite and related species" with the system no. 77.01.05 to be found within the sub-section of " Real Zeolites ".
Crystal structure
Scolecite crystallizes monoclinically in the space group Cc (space group no. 9) with the lattice parameters a = 18.51 Å ; b = 18.97 Å; c = 6.53 Å and β = 90.6 ° and 8 formula units per unit cell .
The crystal structure of scolezite corresponds to that of natrolite (also natrolite structure ) and consists of kinked rings of four with the composition Al 2 Si 2 O 10 , which are linked like a chain in the direction of the fibers by further tetrahedra . Each of these chains is connected in a cross shape to four other chains. Together they form a framework with a continuous, three-dimensional channel system in which H 2 O, Na + , K + , Ca 2+ and other ions can be interchanged .
properties
Skolezite is pyroelectric and piezoelectric , so it builds up an electrical charge when there are temperature changes and deformations occurring at intervals. Some scolecites show yellow to brown fluorescence under UV light .
Education and Locations
(total size: 90 mm × 84 mm. Apophyllite crystal 36 mm × 20 mm)
Like the related minerals mesolite and natrolite, scolezite is a decomposition product of basalt and occurs together with other zeolites and apophyllite as a hydrothermal formation in drusen . Also in some igneous and metamorphic rocks , scolezite occurs as a fissure mineral . Scolecite is formed in the zeolite facies during the low-grade metamorphosis . In addition to the aforementioned apophyllite and other zeolites, calcite , prehnite and stilbit, among others, occur as accompanying minerals .
As a rather rare mineral formation, scolezite can sometimes be abundant at various sites, but overall it is not very common. Around 300 sites are known to date (as of 2012).
Nashik is known for its extraordinary scolezite finds , but also other places in the Indian state of Maharashtra , where crystals up to 20 cm in size have been found. In the 1960s, a large zeolite deposit was discovered near Veranópolis in the Brazilian state of Rio Grande do Sul due to a tunnel construction, also known as the "Das Antas Tunnel" . In addition to 20 cm apophyllites and 25 cm natrolites, there were also up to 20 cm long and 1 cm thick scolecites.
In Germany only individual sites are known so far, including the quarry near Höwenegg (Baden-Württemberg), the Zeilberg (Bavaria), Roßdorf and Ortenberg (Hesse), Sankt Andreasberg (Lower Saxony), Remblinghausen (North Rhine-Westphalia), Arensberg and Lautzenbrücken (Rhineland-Palatinate), Bärenstein (Saxony) and in the basalt quarry "Pflasterkaute" near Eisenach (Thuringia).
In Austria, the mineral occurred mainly in Carinthia and Salzburg in the Hohe Tauern region , but Skolezites were also found in Styria and Tyrol .
In Switzerland, Skolezit was found on the Aargrat in the canton of Bern , in several places in the cantons of Graubünden and Valais and in some places in the cantons of Ticino and Uri .
Other locations are in the Antarctic, Argentina, Australia, Brazil, Bulgaria, Chile, China, Costa Rica, Denmark, Eritrea, France, Iceland, Israel, Italy, Japan, Canada, Madagascar, Namibia, New Zealand, Nicaragua, Norway , Poland, Réunion, Romania, Russia, Sweden, Slovakia, Spain, South Africa, Taiwan, Tanzania, the Czech Republic, Ukraine, Hungary, the United Kingdom (Great Britain) and the United States of America (USA).
use
Skolezite is only rarely offered, especially for collectors, as a gemstone in faceted or spherical cut form .
See also
literature
- 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. 617 .
- Helmut Schrätze , Karl-Ludwig Weiner : Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 911 .
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 791 (first edition: 1891).
Web links
- Mineral Atlas: Skolezite (Wiki)
- realgems.org Skolezite (with picture examples of cut Skolezite)
Individual evidence
- ↑ a b c d e 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. 702 .
- ↑ Webmineral - Scolecite (English).
- ↑ a b c Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 911 .
- ^ A b c John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Scolecite. In: Handbook of Mineralogy, Mineralogical Society of America. 2001 ( handbookofmineralogy.org PDF; 78.5 kB).
- ↑ a b c d e f MinDat - Scolecite (English).
- ↑ a b 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. 273 .
- ↑ a b DC Coombs, A. Alberti, T. Armbruster, G. Artioli, C. Colella, E. Galli, JD Grice, F. Liebau, JA Mandarino, H. Minato, EH Nickel, E. Passaglia, DR Peacor, S. Quartieri, R. Rinaldi, M. Ross, RA Sheppard, E. Tillmanns, G. 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: Mineralogical Magazine. 62, 1998, pp. 533-571.
- ^ AF Gehlen, JN Fuchs: Ueber Werner's Zeolith, Haüy's Mesotype and Stilbite. In: Journal for Chemistry and Physics. Volume 8, 1813 pp. 353–366 ( rruff.info PDF; 751.2 kB)
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 273 .
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 791 (first edition: 1891).
- ↑ The fantastic zeolite deposit "DAS ANTAS". ( Memento from August 4, 2009 in the Internet Archive )
- ↑ Mindat - Localities for scolecite.
- ^ Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 240 .