Thomsonite

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Thomsonite
Thomsonite-280211.jpg
Radial thomsonite, surface brownish colored by elements from the matrix, from Goble Creek , Columbia County (Oregon) , USA
General and classification
other names

Comptonite

chemical formula Na (Ca, Sr) 2 [Al 5 Si 5 O 20 ] · 6-7H 2 O
Mineral class
(and possibly department) 		Silicates and Germanates - framework silicates
System no. to Strunz
and to Dana 		9.GA.10 ( 8th edition : VIII / J.21)
77.01.05.09 and 77.01.05.10
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m 2 / m 2 / m
Room group (no.) Pncn (No. 52)
Lattice parameters a  = 13.10  Å ; b  = 13.06 Å; c  = 13.25 Å
Formula units Z  = 4
Twinning occasionally cruciform according to {110}
Physical Properties
Mohs hardness 5 to 5.5
Density (g / cm 3 ) measured: 2.23 to 2.39; calculated: 2.366
Cleavage completely after {010}; good after {100}
Break ; Tenacity uneven to slightly scalloped; brittle
colour colorless, white, yellowish, greenish, pink, brown
Line color White
transparency transparent to translucent
shine Glass luster, pearlescent luster on cleavage surfaces
Crystal optics
Refractive index n  = see properties

Thomsonite is the name of an unspecified mixed crystal with the end members Thomsonite-Ca and Thomsonite-Sr from the mineral class of " silicates and germanates ", which are recognized as independent minerals . Both thomsonites crystallize in the orthorhombic crystal system with the idealized compositions

  • Thomsonite-Ca: NaCa 2 [Al 5 Si 5 O 20 ] • 6H 2 O
  • Thomsonite-Sr: NaSr 2 [Al 5 Si 5 O 20 ] • 6-7H 2 O

Thomsonite as a mixed crystal can also be described with the general formula Na (Ca, Sr) 2 [Al 5 Si 5 O 20 ] · 6-7H 2 O, the elements calcium and strontium in the formula in each case being mutually exclusive represented ( substitution , diadochie), but always in the same proportion to the other components of the mineral. Structurally, thomsonite belongs to the group of zeolites within the framework silicates .

Etymology and history

Thomsonite was first discovered near Old Kilpatrick in the Scottish administrative district of West Dunbartonshire and described in 1820 by Henry James Brooke (1771-1857), who named the mineral after the Scottish chemist Thomas Thomson .

In 1821 David Brewster described a supposedly new type of zeolite as Comptonite after Lord Compton, who brought the samples from Vesuvius . However, in later analyzes, Rammelsberg found that the mineral was identical to thomsonite.

2001 described IV Pekov, EV Lovskaya, AG Turchkova, NV Chukanov, AE Zadov, RK Rastsvetaeva and NN Kononkova with thomsonite-Sr ( IMA 2000-025 ) the strontium-rich end link of the mixed series from the type locality Razvumchorr in the Chibinen on the Russian Kola peninsula.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , thomsonite (Ca) and thomsonite (Sr) belonged to the general division of "tectosilicates (tectosilicates), with zeolites", where they together with gonnardite , mesolite , natrolite , Paranatrolite and scolezite within the zeolite group the subgroup of "fiber zeolites I" with 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), classifies thomsonite (Ca) and thomsonite (Sr) into the more precisely defined division of "tectosilicates" with zeolitic H 2 O ; Family of zeolites ”. This is further subdivided according to the crystal structure, so that the thomsonites can be found according to their structure in the subdivision of "Zeolites with four-ring chains connected via a fifth Si", where they form the unnamed group 9.GA.10 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , also classifies the Thomsonite under the category of "framework silicates: zeolite group". Here they are together with natrolite, tetranatrolite , paranatrolite, mesolite, skolezite, edingtonite , gonnardite, cowlesite and nabesite in the " natrolite and related species " with the system no. 77.01.05 to be found in the subsection "Real Zeolites".

Crystal structure

Thomsonite crystallizes orthorhombically in the space group Pncn (space group no. 52) with the lattice parameters a  = 13.10  Å ; b  = 13.06 Å and c  = 13.25 Å and 4 formula units per unit cell .

properties

morphology

Thomsonite develops needle-like, prismatic or tabular crystals , which are usually arranged in tufted, radial to spherical or cluster-like aggregates of up to 12 centimeters in size.

Optical properties

In its pure form, thomsonite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a yellowish, greenish, pink or brown color, the transparency decreasing accordingly. However, Thomsonite always leaves a white line on the marking board . The crystal surfaces have a glass-like sheen , whereas the cleavage surfaces have a more mother-of-pearl shimmer .

mineral Refractive indices Birefringence Optical character Optical axis angle
Thomsonite approx n α  = 1.511 to 1.530 n β  = 1.513 to 1.532 n γ  = 1.516 to 1.545 δ = 0.005 to 0.015 biaxial positive 44 ° to 75 °
Thomsonite Sr n α = 1.528 n β = 1.532 n γ = 1.540 δ = 0.012 biaxial positive 62 °

Modifications and varieties

As Faröelith (English also Faröelite or Faroelite ) is a radialfaserige globular Thomsonit- variety of the Faroe Islands named.

Education and Locations

Spherical thomsonite aggregate from Aurangabad, Maharashtra, India (8.3 × 6.6 × 5.6 cm)
Calcite - druse with white thomsonite balls, some of which are overgrown with fibrous thomsonite crystals, from Goble, Columbia County (Oregon) , USA (size: 30 × 25 × 18 mm)
Geode partly filled with salmon-colored Thomsonite Ca crystals from Ortisei in Val Gardena (Italian Ortisei ), South Tyrol (size: 8.0 × 6.0 × 4.2 cm)

The minerals of the Thomsonite group are formed in basalts and occasionally in granitic pegmatites , where mostly in paragenesis with other zeolites , but also with calcite , datolite , prehnite and / or quartz . As a rather rare mineral formation, thomsonite can sometimes be abundant at various sites, but overall it is not very common. Around 700 sites are known to date (as of 2013).

The type locality Old Kilpatrick in Scotland and West Paterson in the US state of New Jersey, where radial-ray aggregates of up to 5 centimeters were found, are known due to unusual thomsonite finds. Radial aggregates several centimeters in diameter were also found near Vinařice u Kladna ( Vinařická hora ) in Okres Kladno in the Czech Republic and in the area around Aurangabad (Maharashtra) in the West Indies.

Larger inclusions of massive thomsonite with strikingly colored grains are known from the Upper Lakes . The typical size of thomsonite inclusions is less than half a centimeter. It is difficult to remove them from their matrix undamaged .

Other sites are found in Australia, Costa Rica, Denmark ( Faröerlith ), Germany, France, Iceland, Italy, Japan, Canada, New Zealand, Norway, Austria, Portugal, Russia, Sweden, Switzerland, Spain, South Africa, the Ukraine , in the United Kingdom (Great Britain) and in other states of the USA.

See also

literature

Web links

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

Individual evidence

  1. ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  702 .
  2. ↑ a b 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).
  3. ↑ a b c d Thomsonite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( handbookofmineralogy.org PDF; 79.3 kB).
  4. ↑ a b IMA / CNMNC List of Mineral Names. (November 2012; PDF 8.6 MB; Note: Formula representation: Crystal chemical structural formula according to Strunz).
  5. ^ HJ Brooke: On mesotype, needlestone, and thomsonite. In: Annals of Philosophy. Volume 16, 1820, pp. 193–194 ( rruff.info PDF; 154 kB).
  6. ↑ 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. 331 .
  7. ↑ IV Pekov, EV Lovskaya, AG Turchkova, NV Chukanov, AE Zadov, RK Rastsvetaeva, NN Kononkova: Thomsonite-Sr (Sr, Ca) 2 Na [Al 5 Si 5 O 20 ] · 6-7h 2 O, a new zeolite mineral from the Khibina massif (Kola Peninsula) and the thomsonite-Ca-thomsonite-Sr isomorphous series. In: Zapiski Vserossiyskogo Mineralogicheskogo Obshchestva. Volume 130, No. 4, pp. 46-55 ( mineralogicalassociation.ca ( memento of March 4, 2016 in the Internet Archive ) PDF; 35.7 kB).
  8. ↑ Mindat - Thomsonite-Approx.
  9. ^ Mindat - Thomsonite-Sr.
  10. ↑ Mindat - Faroelite.
  11. ^ Mindat - Thomsonite. (Subgroup)
  12. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 273 .
  13. ↑ Mindat - localities for Thomsonite.