Gmelinite

• Groddeckit

Gmelinite is the collective name for an unspecified particular mineral of a group of chemically very similar minerals, consisting of the of the International Mineralogical Association (IMA ) recognized end members gmelinite Ca, K and gmelinite gmelinite Na. All end members crystallize in the hexagonal crystal system with the following chemical composition:

• Gmelinite Na: Na 4 [ Al4Si8O24 ] · 11H2O (empirical formula: ( Na7.61Ca0.03K0.16 ) [ Al7.41Si16.49O48 ] · 21.51H2O )

• Gmelinite Ca: Ca2 [ Al4Si8O24 ] · 11H2O (empirical formula: ( Ca2.06Sr1.35Na0.78K0.11 ) [ Al7.82Si16.21O48 ] · 23.23H2O )

• Gmelinite K: K4 [ Al4Si8O24 ] · 11H2O (empirical formula: ( K2.72Ca1.67Sr0.39Na0.22Mg0.13 ) [ Al7.79Si16.32O48 ] · 23.52H2O )

So there are a chemical point of hydrous sodium, calcium or potassium aluminosilicates belonging structurally to the framework silicates and are counted as such to the group of zeolites within the mineral class of " silicates and Germanates ".

Gmelinite usually develops tabular, pyramidal or rhombohedral crystals with glass-like sheen on the surfaces, but also occurs in the form radialstrahliger or granular mineral aggregates. In its pure form it is colorless and transparent. But it may also appear white and by foreign admixtures a yellowish, greenish or pale orange to salmon- red color to assume the transparency decreases accordingly. Through multiple refraction due to lattice defects or polycrystalline training

Etymology and history

Was first discovered gmelinite at Monte Nero, near the municipality of San Pietro Mussolino in the northeastern Italian province of Vicenza (Veneto ) and described in 1825 by David Brewster, who named the mineral after the famous chemists and pharmacists Christian Gottlob Gmelin ( 1792-1860 ).

Gmelinite Ca was also first discovered on Monte Nero and 1997 by Douglas S. Coombs et al. described. Due to this discovery, the gmelinite described by Brewster in 1997/98 as part of a general Überbeitung the zeolite nomenclature by Coombs et al. renamed as sodium- rich end member in gmelinite Na. As a third possible, first hypothetical end member of the series gmelinite gmelinite -K has been proposed. The crystal structure of gmelinite Na was first determined in 1966 by K. Fischer, 1982, however, by Ermanno Galli et al. redefined. The structure of gmelinite K 1990 by Giovanna Vezzalini et al. redefined.

As a natural mineral formation gmelinite K was founded in 1999 on Alluaiw also discovered on the Russian Kola Peninsula for the first time in the Lovozero tundra massif and by AP Khomyakov, LI Polezhaeva and Yu. A. Malinovskiy described. The IMA was the mineral under the Accession no. 1999-039 registered, tested and recognized as its own. The publication of the original description, followed in 2001 in the book published by the Mineralogical Society of America magazine " American Mineralogist ".

Classification

Already in the outdated, but partly still in use 8th edition of the mineral classification by Strunz included the Gmelinite to the mineral class of " silicates and Germanates " and then to the Department of " framework silicates ( tectosilicates ), with zeolites " where they together with Bellbergit, chabazite Ca, chabazite -K, chabazite -Na, Sr - chabazite, erionite - Ca, K - erionite, erionite -Na, Ca - Levyn, Levyn -Na, mazzite Mg, Na mazzite, offretite Perlialith, Tschernichit and Willhendersonit the " subgroup of Würfelzeolithe I" with the system no. VIII/J.26 formed within the zeolite group.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Gmelinite also in the department of " framework silicates ( tectosilicates ) with zeolitic H 2 O; Family of zeolites " one. However, this is further subdivided according to the framework structure, so that the Gmelinite can be found according to their construction in the subdivision " chains of five rings ", where they form the unnamed group 9.GD.05.

The mainly common in English-speaking classification of minerals according to Dana assigns the Gmelinite in the class of " silicates and Germanates " and there in the department of " framework silicates: Zeolite - group " field. Here they are in the " chabazite and related species " with the system no. 77.01.02 found within the subdivision "Real zeolites ".

Education and Locations

Gmelinite formed in cavities of sodium, calcium and / or potassium-containing volcanic rocks such as basalt or pegmatite. Accompanying minerals other zeolites, but also aragonite, calcite, cancrinite, nepheline, quartz, sodalite and other minerals may occur.

As a rather rare mineral formation Gmelinite at different sites can be abundant in some cases, a total of these minerals, however, are not widespread. Total so far (as of 2013) are around 160 localities known as. In addition to the applicable gmelinite Na and gmelinite C type locality Monte Nero and other places in the Veneto region, these minerals were still at Mount Caliella at Palagonia evident in Sicily. Gmelinite K could except at its type locality Alluaiw in Russia so far only be found in San Giorgio di Perlena in the Italian province of Vicenza (Veneto )

In Germany gmelinite is so far known only from Sankt Andreas mountain in Lower Saxony and the Malscheid at Herdorf in North Rhine -Westphalia.

Other localities lie including Australia, Greenland, Canada, Israel, Kazakhstan, Japan, Madagascar, New Zealand, Norway, Spain, Czech Republic, Ukraine, Hungary, the United Kingdom ( UK), the United States of America (USA ) and Cyprus.

Crystal structure

All Gmelinite crystallize in the space group P63/mmc hexagonal ( Raumgruppen-Nr. 194 ) with the following lattice parameters at each one formula unit per unit cell:

• Gmelinite Na: a = 13.756 (5 ) Å and c = 10.048 (5 ) Å
• Gmelinite Ca: a = 13.800 (5 ) Å and c = 9.964 (5 ) Å
• Gmelinite -K: a = 13.621 (3) Å and c = 10.254 (1) Å