Aragonite
| Aragonite | |
|---|---|
 |
|
| General and classification | |
| other names |
Arragonian apatite |
| chemical formula | Ca [CO 3 ] |
|
Mineral class (and possibly department) |
Carbonates and nitrates |
|
System no. to Strunz and to Dana |
5.AB.15 ( 8th edition : Vb / A.04) 01/14/03/01 |
| Similar minerals | Calcite , vaterite , barite , gypsum |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Space group | Pmcn (No. 62, position 5) |
| Lattice parameters | a = 4.96 Å ; b = 7.97 Å; c = 5.74 Å |
| Formula units | Z = 4 |
| Twinning | often after {110}, cyclic triplets or multiples, polysynthetic multiples |
| Physical Properties | |
| Mohs hardness | 3.5 to 4 |
| Density (g / cm 3 ) | measured: 2.95; calculated: 2.930 |
| Cleavage | imperfect after {110} and {011}, indistinct after {010} |
| Break ; Tenacity | clamshell; brittle |
| colour | colorless, white, gray, yellow, red, green, violet, blue |
| Line color | White |
| transparency | transparent to opaque |
| shine | Glass gloss, greasy gloss on crack and fracture surfaces |
| Crystal optics | |
| Refractive indices |
n α = 1.529 to 1.530 n β = 1.680 to 1.682 n γ = 1.685 to 1.686 |
| Birefringence | δ = 0.156 |
| Optical character | biaxial negative |
| Axis angle | 2V = 18 ° to 19 ° (measured); 16 ° to 18 ° (calculated) |
| Pleochroism | unavailable |
| Other properties | |
| Chemical behavior | soluble in HCl with release of CO 2 |
| Special features | Luminescence |
Aragonite is a frequently occurring mineral from the mineral class of " carbonates and nitrates ". It crystallizes in the orthorhombic crystal system with the composition Ca [CO 3 ], so it is chemically a calcium carbonate .
Aragonite crystallizes in various forms. Prismatic crystals occur as well as mineral aggregates , which can be spherical or oolithic , banded, columnar and dendritic (tree-like) as well as parallel-fiber, radial-ray or needle-like. Undamaged crystal surfaces have a glass-like gloss , whereas cracks and fractures have a greasy sheen .
In its pure form, aragonite 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 gray, yellow, red, green, violet or blue color, the transparency decreasing accordingly.
Aragonite is the eponymous mineral of a group of minerals with a similar structure and / or composition, the aragonite group .
Etymology and history
The mineral was described by Abraham Gottlob Werner in 1796 and named by him after its place of discovery in the province of Aragon in northeastern Spain .
classification
In the outdated 8th edition of the mineral classification according to Strunz , the aragonite belonged to the common mineral class of "carbonates, nitrates and borates" and there to the department of "anhydrous carbonates without foreign anions ", where it named the "aragonite series" with the system -No. Vb / A.04 and the other members alstonite , cerussite , strontianite and witherite as well as in the appendix with barytocalcite .
In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. V / B.04-10 . In the "Lapis system" this also corresponds to the section "Anhydrous carbonates [CO 3 ] 2− without foreign anions", where aragonite together with alstonite, barytocalcite, cerussite, olekminsite , paralstonite , strontianite and witherite form the "aragonite group" (As of 2018).
The 9th edition of Strunz's mineral systematics , valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns aragonite to the newly defined class of "carbonates and nitrates" (the borates form a separate class here), but there also in the section of “carbonates without additional anions; without H 2 O “. This is further subdivided according to the affiliation of the cations to certain element families, so that the mineral can be found according to its composition in the sub-section "alkaline earth (and other M 2+ ) carbonates", where it is only found together with cerussite, strontianite and witherite the "aragonite group" with the system no. 5.AB.15 forms.
The systematics of minerals according to Dana , which is common in the English-speaking world , assigns aragonite to the common class of "carbonates, nitrates and borates" and there in the department of "anhydrous carbonates", like the outdated Strunz system. Here it is also together with cerussite, strontianite and withitherite in the " aragonite group (Orthorhombic: Pmcn) " with the system no. 01/14/03 to be found in the sub-section "Anhydrous carbonates with simple formula A + CO 3 ".
Crystal structure
Aragonite crystallizes orthorhombically in the space group Pmcn (space group no. 62, position 5) with the lattice parameters a = 4.96 Å , b = 7.97 Å and c = 5.74 Å as well as four formula units per unit cell .
properties
Pure aragonite is either colorless or white. It can also be gray to brownish, yellowish, reddish, greenish, bluish or purple in color due to foreign admixtures or impurities. Aragonite has a density of 2.95 g / cm³ and a Mohs hardness of 3.5 to 4.5. Except for one variety of aragonite, all are opaque.
Aragonite shows luminescence , but the minerals behave differently depending on where they were found. Aragonites are found in Agrigento , which glow pink under UV light and then fluoresce green . Aragonites from Tsumeb shine light yellow to greenish.
Aragonite dissolves easily in acids , releasing carbon dioxide . Weak acids such as boric acid , acetic acid or citric acid can damage the crystal. Aragonite is more soluble in carbon dioxide-saturated water than calcite and can lead to an undersaturation of aragonite in the oceans.
Modifications and varieties
Aragonite is one of three naturally occurring modifications of calcium carbonate (Ca [CO 3 ]). The other modifications are calcite (calcite) and vaterite . The most stable of the three modifications is calcite, which occurs naturally as limestone , chalk , marble and lime sinter ( onyx marble ).
There are several color and shape varieties of aragonite:
- Iron flower : coral-like growth with predominantly white or white-gray color; seldom light blue to pale blue-green iron flowers are also found
- Pea stone or pisolite : mostly concentric shells or radial spheres with a predominantly white-gray color
- Nicholsonite : due to the addition of Smithsonite (Zn [CO 3 ]) mostly white, yellowish, greenish or slightly pink
- Mother of pearl : variable
- Air stone : wavy, usually white, gray, yellowish or reddish banded calcareous sinter
- Sr-aragonite : aragonite containing strontium
- Tarnowitzite ( Plumboan Aragonite ): mostly white, gray to black or yellow colored by finely distributed inclusions of cerussite (Pb [CO 3 ])
- Zeiringite : aragonite colored turquoise blue to turquoise green by aurichalcite
There are many minerals similar to aragonite such as barite , gypsum , calcite and quartz .
"Eisenblüte" from Styria (exhibited in the Natural History Museum Vienna )
"Pea stone" (Pisolith)
Banded crusty sintered lime (Karlsbader hot spring stone)
"Zeiringit" (bluish aragonite)
Education and Locations
education
Under normal circumstances (20 ° C and atmospheric pressure) aragonite is actually only metastable , the stable phase is calcite . The presence of a solvent or the application of minimal pressure, for example in a mortar, are sufficient to convert aragonite into calcite. At higher temperatures, the conversion happens very quickly. Only at high pressure, under the conditions of high pressure / low temperature metamorphosis , is aragonite stable. Therefore, one rarely finds a rock with aragonite, the aragonite marble is an exception .
Aragonite is rarely deposited in fresh water, so the individual occurrences are characteristic of marine environments. In contrast to most other mineral substances, calcium occurs less often there than in fresh water, as numerous organisms extract the mineral from the water in order to build up their calcareous shells and skeletons. As a result, the ratio of magnesium to calcium has shifted more and more to the side of magnesium over the course of the geological ages, and since magnesium favors the formation of aragonite over that of calcite, aragonite is now preferably formed in the marine environment. In addition to magnesium, traces of other metals such as strontium , lead , barium and calcium sulfate as well as temperatures above 50 degrees Celsius shift the equilibrium to the side of aragonite. However, over longer periods of time it changes into the more stable calcite, which is why aragonite is rare in old carbonate rocks.
The mineral forms either hydrothermally or as a new formation from decomposing Ca-containing rocks (so-called "iron bloom"). In nature, aragonite often occurs when sintering occurs in the vicinity of calcareous and hot springs. It also occurs in the cavities of effusion rocks ( volcanic rocks ) as "iron bloom", in thermal springs as "hot spring stone" and "pea stone". Deposits in water pipes, water pipes and kettles are often made of aragonite.
Aragonite is also the main component of mother- of- pearl and therefore of the pearls that are formed by the shell of the shell . The skeleton of the hard corals is also made of aragonite.
As a frequent mineral formation, aragonite can be found in many localities, whereby so far (as of 2013) around 2800 localities are known.
Locations
Aragonite is found in the Municipio Corocoro in Bolivia , the Erzberg in Austria , Špania Dolina , Podrečany and Ochtiná ( Ochtina Aragonite Cave ) in Slovakia , Cianciano in Italy , Tarnobrzeg in Poland and Molina de Aragón in Spain .
In the Czech Republic , aragonite occurs on the one hand as a microcrystalline hot spring stone at spring outlets in Karlovy Vary , but also in the form of larger crystals on the Číčov in the Bohemian Central Uplands . The Karlsbader hot spring stone deposits were already described by Johann Wolfgang von Goethe .
The possibly largest iron blossoms with diameters of sometimes more than 1.20 m - the largest of these so far known as "Hydra" structures has a diameter of 1.50 m - were found in the Windloch cave in Mühlenberg in Oberberberg, which was discovered in March 2019 .
Synthetic manufacture
In the Biorock technology , aragonite is extracted from the sea together with brucite through mineral accretion on low-current steel.
use
Aragonite is used as a gem stone , which is sensitive due to its brittleness and good cleavage.
In the Bahamas and the Bermuda Islands in particular, aragonite sands have been forming in the tidal range for several thousand years and are suitable for industrial use. The deposits are extracted with an excavator and used to produce cement.
Manipulations and imitations
Aragonite gemstones are stabilized with the help of synthetic resin , since aragonite is quite sensitive to acids and machining, and it is also said to increase its gloss. For fashion reasons, aragonites are also offered colored. Both procedures must be specified for consumer protection reasons.
Aragonite is often used as an imitation base for chalcedony , calcite and jade .
Banded aragonite is usually sold under misleading trade names as California onyx , Mexican onyx or Turkish onyx (see onyx marble ).
Esoteric
As already described, aragonite and calcite can form as deposits in hot water installations or pipes. Through the use of magnetic fields, the aragonite crystals should not be able to form or deposit on the wall. The mode of operation of such devices for decalcification can be viewed as questionable according to the current state of knowledge, since neither the carbonate anions nor the calcium ions are paramagnetic or ferromagnetic . From a physicochemical point of view, the postulated active principles are not possible (see also physical water softening ).
See also
literature
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 573 (first edition: 1891).
- Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 65 .
- Petr Korbel, Milan Novák: Mineral Encyclopedia (= Villager Nature ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 119 .
- Bernhard Bruder: Beautified stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 56, 74 .
Web links
- Mineral Atlas: Aragonite (Wiki)
- Geology Info - Properties of Minerals. Crystal system ( Memento from October 22, 2016 in the Internet Archive )
- Gemstone etiquette - aragonite as a gemstone. In: beyars.com. Retrieved June 24, 2020 .
Individual evidence
- ↑ Abraham Gottlob Werner : History, characteristics, and brief chemical investigation of the apatite. IV. Brief message from the so-called Arragonian apatites . In: Bergmannisches Journal . tape 1 , 1788, pp. 76–96 ( rruff.info [PDF; 1.4 MB ; accessed on June 24, 2020]).
- ↑ David Barthelmy: Aragonite Mineral Data. In: webmineral.com. Retrieved June 24, 2020 .
- ^ A b c Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 287 (English).
- ↑ a b c d Aragonite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 68 kB ; accessed on June 24, 2020]).
- ↑ a b c d e Aragonite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 24, 2020 .
- ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 706 .
- ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
- ↑ Ernest H. Nickel , Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF; 1.82 MB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed June 24, 2020 .
- ↑ Gabriela Negrete-García, Nicole S. Lovenduski, Claudine Hauri, Kristen M. Krumhardt, Siv K. Lauvset: Sudden emergence of a shallow aragonite saturation horizon in the Southern Ocean . In: Nature Climate Change . tape 9 , 2019, pp. 313 , doi : 10.1038 / s41558-019-0418-8 (English, []).
- ↑ Tarnowitzite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 24, 2020 .
- ↑ a b Wolfgang F. Tegethoff: Calcium carbonate from the Cretaceous into the 21st century . Springer, Basel 2013, ISBN 978-3-0348-8259-0 , pp. 15 ( limited preview in Google Book search).
- ↑ Localities for aragonite. In: mindat.org. Hudson Institute of Mineralogy, accessed June 24, 2020 .
- ↑ Find location list for aragonite in the Mineralienatlas and Mindat , accessed on June 24, 2020.
- ^ Johannes Baier: Goethe and the thermal springs of Karlovy Vary (Karlsbad, Czech Republic) . In: Annual reports and communications from the Upper Rhine Geological Association . tape 94 , 2012, p. 87-103 , doi : 10.1127 / jmogv / 94/2012/87 ( researchgate.net [PDF; 372 kB ; accessed on June 24, 2020]).
- ↑ Ulrich Brämer: Spectacular giant crystal finds in the wind hole. In: akkh.de. June 24, 2020, accessed June 24, 2020 .
- ↑ Torsten Sülzer: Gigantic iron blossoms in Engelskirchen: Researchers make sensational discovery in the wind hole. In: rundschau-online.de. Oberbergische Volkszeitung , accessed on June 24, 2020 .
- ↑ Stephan Matthiesen, Ralph Puchta: Kalk - the ghost in the water pipe. In: gwup.org. Society for the Scientific Investigation of Paraweek eV, February 1997, accessed on June 24, 2020 .