Hexahydrite
| Hexahydrite | |
|---|---|
 |
|
| General and classification | |
| other names |
|
| chemical formula | Mg [SO 4 ] • 6H 2 O |
|
Mineral class (and possibly department) |
Sulphates (selenates, tellurates, chromates, molybdates and wolframates) - sulphates containing water without foreign anions |
|
System no. to Strunz and to Dana |
07.CB.25 ( 8th edition : VI / C.05) 06/29/08/01 |
| Similar minerals | Kieserite , pentahydrite , epsomite |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / c (No. 15) |
| Lattice parameters |
a = 10.11 Å ; b = 7.21 Å; c = 24.41 Å β = 98.3 ° |
| Formula units | Z = 8 |
| Frequent crystal faces | {001} |
| Twinning | according to {001} and {110} |
| Physical Properties | |
| Mohs hardness | 2 to 2.5 |
| Density (g / cm 3 ) | measured: 1.757; calculated: 1.745 |
| Cleavage | completely after {100} |
| Break ; Tenacity | shell-like |
| colour | colorless, white, same light green |
| Line color | White |
| transparency | transparent to opaque |
| shine | Pearl to glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.426 n β = 1.453 n γ = 1.456 |
| Birefringence | δ = 0.030 |
| Optical character | biaxial negative |
| Axis angle | 2V = 38 ° (measured); 36 ° (calculated) |
| Other properties | |
| Chemical behavior | Easily soluble in water, bitter taste |
Hexahydrite is a rather rare mineral from the mineral class of " sulfates ( and relatives )". It crystallizes in the monoclinic crystal system with the chemical composition Mg [SO 4 ] · 6H 2 O, so from a chemical point of view it is a water-containing magnesium sulfate or a magnesium sulfate hexahydrate .
Hexahydrite usually develops fibrous aggregates and crusty coatings with a pearlescent sheen . Larger crystals are very rare, but then usually show a needle-like to tabular habit and shiny glass surfaces. In its pure form, hexahydrite is colorless and transparent. However, due to multiple light refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a light green color, the transparency decreasing accordingly.
Special properties
Hexahydrite is - similar to epsomite - not stable, that is, under dry conditions it gives off crystal water and if the humidity is too high it dissolves . Hexahydrite is easily soluble in water and gives it a salty-bitter taste, which is why, like Epsomit, it is sometimes referred to as "Epsom salt".
Etymology and history
Hexahydrite was first discovered on the Bonaparte River in the Canadian province of British Columbia . The mineral was first described in 1911 by Robert AA Johnston, who named it based on its content of six water molecules after the Greek numeral ἑξα- [hexa-] and the word part hydr of hydrates (water-containing substances, Greek ὕδωρ [hydōr] for water) .
classification
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the hexahydrite belonged to the mineral class of "sulfates, selenates, tellurates, chromates, molybdates, wolframates" and there to the department of "hydrous sulfates without foreign anions ", where it was classified as Namesake of the "hexahydrite group" with the system no. VI / C.05 and the other members Bianchit , Chvaleticeit , Ferrohexahydrit , Moorhouseit , Nickelhexahydrit and Retgersit formed.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies hexahydrite in the category of "sulfates (selenates, etc.) without additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With only medium-sized cations”, where the “hexahydrite group” with the system no. 7.CB.25 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns hexahydrite to the class of "sulfates, chromates and molybdates" and there to the "sulfate minerals" category. Here, too, he is the namesake of the " hexahydrite group (room group: C 2 / c ) " with the system no. 06/29/08 to be found in the sub-section “Water-based acids and sulphates with AXO 4 × x (H 2 O)”.
Crystal structure
Hexahydrite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a = 10.11 Å ; b = 7.21 Å; c = 24.41 Å and β = 98.3 ° as well as 8 formula units per unit cell .
Education and Locations
Hexahydrite is a typical secondary mineral that is mainly formed from epsomite due to the loss of part of the crystal water ( dehydration ) . It therefore mostly occurs in the form of efflorescence on magnesium-containing rocks and pit walls or as stalactites in caves. In addition to epsomite, siderotile can also occur as an accompanying mineral . Other sources of hexahydrite are evaporites . Here it can crystallize out of supersaturated magnesium-containing salts . As with epsomite, hexahydrite can form in volcanic fumaroles .
Other magnesium sulfates comparable to hexahydrite are kieserite , pentahydrite and epsomite . These are the respective mono-, penta- or heptahydrates. These minerals can transform into one another by absorbing or releasing water. Occasionally, the corresponding metamorphoses are formed .
As a rather rare mineral formation, hexahydrite can sometimes be abundant at different sites, but overall it is not very common. So far (as of 2013) around 180 sites are known. In addition to its type locality Bonaparte River, the mineral occurred in Canada at Lillooet in British Columbia, at Pine Point in the Northwest Territories , in the nickel mine "Alexo" in Dundonald Township ( Cochrane District ) in Ontario, in the sulphide deposit "Marbridge" near La Motte and the gold-zinc-lead deposit "Montauban" near Mékinac in Québec and in the Dawson mining district in the Yukon Territory.
In Germany, hexahydrite has been found in the Anna mine near Alsdorf, on the Maubacher Bleiberg near Horm in the Eifel, in the Julia mine in the Aachen district and in the copper mines near Marsberg in North Rhine-Westphalia, in the former potash and rock salt works "Brefeld "At Tarthun in Saxony-Anhalt, in mine shaft 371 in the Schlema - Hartenstein area and in the" Dubring "and" Oßling "quarries near Kamenz in Saxony as well as on the sedimentation dump and in the" Lichtenberg "open pit near Ronneburg , in the" Loitsch "quarry at Weida and in the slate quarries near Lehesten near Wurzbach (Saale-Orla district) in Thuringia.
Previously known sites in Austria include the “Holler” quarry near Badersdorf in Burgenland, the “Breitenbuchen” iron deposit near Oberbuchach in the Carinthian municipality of Kirchbach , the rock salt deposit near Dürrnberg and the Leube cement works in Gartenau and the Gadauner Schlucht near Bad Hofgastein in Salzburg, several places in Styria (Admont, Hochlantsch, Langteichengraben, Wolfsgruben, Sunk) and the Bad Ischler Salzberg in Upper Austria.
In Switzerland, the mineral is so far only from Fonte Vittoria near Brissago TI in the canton of Ticino, from the Bex salt mine in the canton of Vaud and in the salt works and quarries near Ayer (Val d'Anniviers) , in the Binn valley , on the Pont du Diable near Conthey and known on Mont Chemin in the canton of Valais.
Other locations are in Egypt, the Antarctic, Argentina, Australia, Chile, China, France, Greece, Greenland, Italy, Japan, Morocco, Macedonia, Mexico, Namibia, Norway, Poland, Russia, Slovakia, Spain, South Africa, Czech Republic, Turkmenistan, Ukraine, Hungary and the United States of America (USA).
use
Like other water-soluble sulfates ( Mirabilit , Kieserit), hexahydrite can be used as a laxative .
See also
literature
- Robt. AA Johnston: Hexahydrite, a new mineral , In: Summary Report of the Geological Survey Branch of the Department of Mines For the Calendar Year 1910 , Volume 26 (1911), pp. 256-257 ( PDF 1.6 MB )
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp. 606 (first edition: 1891).
- 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. 668 .
Web links
- Mineral Atlas: Hexahydrite (Wiki)
- Database-of-Raman-spectroscopy - Hexahydrite
- American-Mineralogist-Crystal-Structure-Database - Hexahydrite
Individual evidence
- ↑ 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. 668 .
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 382 .
- ↑ Webmineral - Hexahydrite
- ↑ a b c d Hexahydrite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 67 kB ; accessed on May 6, 2018]).
- ↑ a b c d e Mindat - Hexahydrite
- ↑ Mindat - Number of localities for hexahydrites
- ↑ List of localities for hexahydrites in the Mineralienatlas and Mindat