Vaterite

Vaterite
	SEM image of some vaterite crystals from the San Vito quarry, Ercolano , Monte Somma, Italy
General and classification
chemical formula	Ca [CO 3 ]
Mineral class; (and possibly department)	anhydrous carbonates without foreign anions - calcite group
System no. to Strunz ; and to Dana	5.AB.20 ( 8th edition : V / B.02) ; 01/14/02/01
Crystallographic Data
Crystal system	hexagonal
Crystal class ; symbol	dihexagonal-dipyramidal; 6 / m 2 / m 2 / m
Space group	P 6 3 / mmc (No. 194)
Lattice parameters	a = 7.135 Å ; c = 8.524 Å
Formula units	Z = 6
Physical Properties
Mohs hardness	3
Density (g / cm 3 )	measured: 2.54; calculated: 2.65
Cleavage	Please complete
Break ; Tenacity	uneven, brittle
colour	colorless, white
Line color	White
transparency	transparent to translucent
shine	Wax gloss
Crystal optics
Refractive indices	n ω = 1.550 ; n ε = 1.650
Birefringence	δ = 0.100
Optical character	uniaxial positive
Other properties
Chemical behavior	Slightly soluble in hydrochloric acid

Vaterite is a rather seldom occurring mineral from the mineral class " carbonates " ( and relatives ). It crystallizes in the hexagonal crystal system with the chemical composition Ca [CO ₃ ] and develops only small, fibrous to prismatic crystals with a hexagonal habit up to about 0.1 mm or spherulitic aggregates , which can be colorless or white in color. The line color is also white.

Etymology and history

Vaterit was named after Heinrich Vater , a German professor of mineralogy and chemistry. This was the first to produce vaterite as a further modification of calcium carbonate. Natural vaterite was first found in 1960 by JDC McDonnell in Ballycraigy, Northern Ireland.

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) the vaterite is assigned to the division of "anhydrous carbonates without foreign anions ". In the 8th edition it together with the minerals calcite , gaspeite , magnesite , otavite , rhodochrosite , siderite , Smithsonite and Sphärocobaltit the Calcitgruppe . However, the new Strunz'sche mineral system classifies here even more precisely according to the type of cations involved . Since the calcium involved is doubly positively charged in the compound, the mineral is listed as a separate subgroup in the subsection "Alkaline earth (and other M ²⁺ ) carbonates".

The systematics of minerals according to Dana leads the vaterite in the subdivision of "anhydrous carbonates with simple formula A ⁺ CO ₃ " where it forms a subgroup of anhydrous carbonates with the composition A ⁺ CO ₃ together with the crystal-chemically similar mineral Gregoryite .

Crystal structure

Vaterite crystallizes in the hexagonal crystal system in the space group P 6 ₃ / mmc (space group no. 194) with the lattice parameters a = 7.135 Å and c = 8.524 Å as well as six formula units per unit cell . Template: room group / 194

In vaterite is ordered hexagonal CO switch ₃ groups [8] -fold coordinated calcium - ion from, so that each calcium ion centrally located eight ions of CO ₃ is surrounded group.

Modifications and varieties

Vaterite is a metastable modification of calcium carbonate that arises from aqueous, highly supersaturated solutions at a temperature below 400 ° C. Along with calcite and aragonite, it is the rarest of the three natural modifications that crystallize in different crystal structures with the same chemical composition . At temperatures above 400 ° C, the metastable vaterite transforms into the more stable calcite.

Education and Locations

Vaterites from the San Vito site (Ercolano, Italy) only form microcrystals with a size of less than 2 mm. This crystal is epitaxially grown inside with aragonite . The formation of twins is clearly visible at the end of the crystal.

Vaterite is formed by hydrothermal deposition at low temperatures in mineral-rich sources , but also in organic tissues and is a component of gallstones and kidney stones . The mineral also plays a role in the mineralization of organic matter. Besides calcite and aragonite, accompanying minerals include tobermorite , hydrogranate and kaolinite .

As a rather rare mineral formation, vaterite has so far (status: 2011) been detected at around 30 sites worldwide.

In Germany, the mineral was found near Oberwolfach in Baden-Württemberg, Oberschulenberg / Schulenberg in the Upper Harz in Lower Saxony and several places in the Eifel .

The only place where vaterite was found so far for Austria, Hopffeldboden in Obersulzbachtal (Salzburg), turned out to be a misidentification. More recent investigations of the same material showed that it was calcite .

Other sites are Liawenee in the Australian Central Highlands Municipality , Yuhang in China, Mont Saint-Hilaire and Saint-Honoré (Québec) in Canada, the Hatrurim Formation in the West Bank , San Vito / Ercolano on Monte Somma in Italy, Ashoro (Hokkaidō) in the Japanese sub-prefecture Tokachi , Kombat in Namibia, Siemianowice Śląskie in Poland, Hunedoara in Romania, Kola and Tscheljabinsk in Russia, Hotazel in the South African Kalahari , Táska in the Hungarian county of Somogy as well as Phoenix (Arizona) , Osceola (Michigan) , Cornudas (New Mexico) and Carthage, Tennessee in the US.

In Portland cement and marble of the Duomo of Florence and in drilling muds in oil exploration and statoliths of herring and piranhas vaterite was found.

literature

Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 569 .

Web links

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

Mineral Atlas: Vaterite (Wiki)

Webmineral - Vaterite

Handbook of Mineralogy - Vaterite (English, PDF 68 KB)

American-Mineralogist-Crystal-Structure-Database - Vaterite (crystal structure database )

Individual evidence

↑ ^a ^b ^c ^d ^e Vaterite at mindat.org (engl.)
^ John Johnston: The several forms of calcium carbonate. In: American Journal of Science. 1916, 4, 41, pp. 473-512 ( abstract ).
↑ JDC McDonnell: vaterite from Ballycraigy, Larne, Northern Ireland. In: Mineralogical Magazine. 1960, 32, pp. 535-545, abstract in: Michael Fleischer: New Mineral Names, Vaterite. In: American Mineralogist. 1960, 45, p. 1316 ( pdf ).
^ List of minerals according to Dana at webmineral.com
↑ ^a ^b entry on vaterite. In: Römpp Online . Georg Thieme Verlag, accessed on June 19, 2014.
↑ Martin Okrusch, Siegfried Matthes: Mineralogie: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3 , pp. 65 .
↑ Uwe Kolitsch: Vaterite vom Hopffeldboden, Obersulzbachtal: an incorrect determination , in: Neue Mineralfunde aus Österreich LX. Carinthia , G. Niedermayr et al. 2011, pp. 155–156

[Mindat-1] Vaterite at mindat.org (engl.)

[2] John Johnston: The several forms of calcium carbonate. In: American Journal of Science. 1916, 4, 41, pp. 473-512 ( abstract ).

[3] JDC McDonnell: vaterite from Ballycraigy, Larne, Northern Ireland. In: Mineralogical Magazine. 1960, 32, pp. 535-545, abstract in: Michael Fleischer: New Mineral Names, Vaterite. In: American Mineralogist. 1960, 45, p. 1316 ( pdf ).

[4] List of minerals according to Dana at webmineral.com

[Römpp-5] try on vaterite. In: Römpp Online . Georg Thieme Verlag, accessed on June 19, 2014.

[6] Martin Okrusch, Siegfried Matthes: Mineralogie: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3 , pp. 65 .

[7] Uwe Kolitsch: Vaterite vom Hopffeldboden, Obersulzbachtal: an incorrect determination , in: Neue Mineralfunde aus Österreich LX. Carinthia , G. Niedermayr et al. 2011, pp. 155–156