Vaterite
Vaterite is a rarely occurring mineral from the mineral class " carbonates " ( and relatives ). It crystallizes in the hexagonal crystal system with the chemical composition Ca [ CO3 ] and develops only small fibrous and hexagonal prismatic crystals habit to about 0.1 mm or spherulitic aggregates, which may be colorless or white in color. The stroke color is also white.
Special Features
At temperatures above 400 ° C, the metastable vaterite transforms into the more stable calcite.
Etymology and history
Vaterite was named after Henry 's father, a German professor of mineralogy and chemistry. This turned vaterite calcium carbonate as a further modification fro the first time. Natural vaterite was the first time in 1960 by JDC McDonnell found in Ballycraigy in Northern Ireland.
Classification
In the old ( 8th edition ) and new classification of minerals according to Strunz ( 9th edition ) of the Department of vaterite is assigned to " anhydrous carbonates without foreign anions ." In the 8th edition of it, together with the minerals calcite, Gaspéit, magnesite, Otavit, rhodochrosite, siderite, smithsonite and Sphärocobaltit the Calcitgruppe. The new Strunz'sche Mineral classification divided here but even more precisely on the nature of the cations involved. Since the involved calcium is doubly positively charged in the connection, the mineral is available as a separate subgroup in accordance with the subdivision " alkaline-earth (and other M2 ) carbonates ".
The classification of minerals according to Dana leads the vaterite in the subdivision of " anhydrous carbonates with a simple formula A CO3 " where it forms a subset of the anhydrous carbonates with the composition A CO3 and the crystal chemically similar mineral Gregoryit.
Modifications and varieties
Vaterite is a metastable form of calcium carbonate, which is produced from aqueous, highly supersaturated solutions at a temperature below 400 ° C. It is adjacent to calcite and aragonite, the rarest of the three natural modifications which crystallize with the same chemical composition in different crystal structures.
Education and Locations
Vaterite formed by hydrothermal deposition at low temperatures in mineral-rich sources, but also in organic tissues and is a constituent of gallstones and kidney stones dar. In addition, the mineral plays a role in the mineralization of organic matter. Accompanying minerals are calcite and aragonite in addition, you still tobermorite hydrogarnet and kaolinite.
In Germany, the mineral, among others at Oberwolfach in Baden- Württemberg, Oberschulenberg / Schulenberg found in the Upper Harz in Lower Saxony and several places in the Eifel.
The only previously specified for Austria locality for vaterite, Hopffeldboden in Obersulzbachtal (Salzburg), turned out to be false identification. Recent studies of the same material showed that it was a question of calcite.
Other localities are Liawenee in the Australian Central Highlands Municipality, Yuhang in China, Mont Saint- Hilaire and Saint- Honoré (Quebec ) in Canada, the Hatrurim formation in the West Bank, San Vito / Ercolano at Monte Somma in Italy, Ashoro ( Hokkaido ) in the Japanese sub-prefecture of Tokachi, Kombat in Namibia, Siemianowice Śląskie in Poland, Hunedoara in Romania, Kola and Chelyabinsk in Russia, Hotazel in the South African Kalahari, Táska in the Hungarian county of Somogy and Phoenix (Arizona ), Osceola (Michigan), Cornudas (New Mexico) and Carthage (Tennessee ) in the USA.
Also in Portland cement and marble in the Duomo of Florence, and in drilling muds in oil wells, and the statoliths of herring and piranhas were found vaterite.
Crystal structure
Vaterite crystallized in the hexagonal crystal system in space group P63/mmc with lattice parameters a = 7.135 Å and c = 8.524 Å and six formula units per unit cell.
In vaterite is hexagonally ordered CO3 groups alternate with - fold coordinated calcium ions, so that each calcium ion is surrounded by eight centrally located ion the CO3 group.