Thomsonite

• Comptonit

Thomsonite -Sr: N? = 1.528 nβ = 1.532 N r = 1.540

Thomsonit is the name of an unnamed mixed crystal with the recognized as a distinct mineral end members Thomsonit - Ca and Sr - Thomsonit from the mineral class of " silicates and Germanates ". Both Thomsonite crystallize in the orthorhombic crystal system with the idealized compositions

• Thomsonit - Ca: NaCa2 [ Al5Si5O20 ] · 6H2O
• Thomsonit -Sr: NaSr2 [ Al5Si5O20 ] · 6- 7H2O

Thomsonit as a mixed crystal can Na ( Ca, Sr ) 2 [ Al5Si5O20 ] · are also having the general formula described 6- 7H2O, where indicated in the parentheses of the elements calcium and strontium can be represented each other in the formula (substitution, Diadochie ) but always in the same proportions are to the other components of the mineral. Structurally Thomsonit belongs within the framework silicates to the group of zeolites.

In its pure form Thomsonit is colorless and transparent. But it can also appear white and accept by foreign admixtures a yellowish, greenish, pink, or brown color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly. On the dash board but Thomsonit always leaves a white line.

Thomsonit developed acicular, prismatic or tabular crystals with glass-like sheen on the surfaces, which are usually arranged in wispy, radialstrahligen to spherical or botryoidal aggregates of up to 12 centimeters in size.

Etymology and history

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

1821 David Brewster described a supposedly new of zeolite as Comptonit to Lord Compton, who brought the samples from Vesuvius. However Rammelsberg found in subsequent analyzes that the mineral with Thomsonit was identical.

Described in 2001 IV Pekov, EV Lovskaya, AG Turchkova, NV Chukanov, AE Zadov, RK Rastsvetaeva and NN Kononkova with Thomsonit -Sr (IMA 2000-025 ), the strontium- rich end member of the mixing series from the type locality Raswumtschorr in the Chibinen on the Russian Kola Peninsula.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz Thomsonit (Ca ) and Thomsonit -heard ( Sr) to the general ward of the " framework silicates ( tectosilicates ), with zeolites " where they together with Gonnardite, Mesolith, Natrolite, Paranatrolith and Skolezit within the zeolite group the subset of " Faserzeolithe I" with the system no. VIII/J.21 formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns Thomsonit (Ca ) and Thomsonit - ( Sr) in the Department of precisely defined " framework silicates ( tectosilicates ) with zeolitic H 2 O; Family of zeolites " one. This is also further divided according to the crystal structure, so that the Thomsonite can be found according to their construction in the subdivision of " zeolites with four - ring chains connected via a fifth Si ", where they form the unnamed group 9.GA.10.

The mainly common in English-speaking classification of minerals according to Dana assigns the Thomsonite in the department of " framework silicates: Zeolite - group " field. Here they are along with Natrolite, Tetranatrolith, Paranatrolith, Mesolith, Skolezit, edingtonite, Gonnardite, Cowlesit and Nabesit in the " Natrolite and related species " with the system no. 77.01.05 found within the subdivision "Real zeolites ".

Modifications and varieties

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

Education and Locations

The minerals of the Thomsonit group formed in basalts and occasionally in granitic pegmatites, where. Mostly in paragenesis with other zeolites, but also with calcite, Datolith, prehnite and / or quartz As a rather rare mineral formation Thomsonit can indeed be abundant in part to different sites, overall it is not very common. So far (as of 2013) are considered to be known around 700 localities.

Known due to exceptional Thomsonitfunde include the type locality Old Kilpatrick in Scotland and West Paterson in the U.S. state of New Jersey, where radiating aggregates were up to 5 centimeters found. Also radiating aggregates of several centimeters in diameter were found near Vinařice u Kladna ( Vinařická hora ) in Czech Okres Kladno and the area around Aurangabad ( Maharashtra ) in the West Indies.

Larger inclusions of solid Thomsonite with striking colored veins are known from the Upper Lakes. The typical size of Thomsoniteinschlüssen is less than half a centimeter. It is difficult to detach from their intact matrix.

Other sites are located including Australia, Costa Rica, Denmark ( Faröerlith ), Germany, France, Iceland, Italy, Japan, Canada, New Zealand, Norway, Austria, Portugal, Russia, Sweden, Switzerland, Spain, South Africa, Ukraine, the United Kingdom ( UK) and in other U.S. states.

Crystal structure

Thomsonit crystallizes in the orthorhombic space group Pncn ( Raumgruppen-Nr. 52) with the lattice parameters a = 13.10 Å; b = 13.06 Å and c = 13.25 Å and four formula units per unit cell.