Picromerite
| Picromerite | |
|---|---|
 |
|
| General and classification | |
| other names |
Schönit |
| chemical formula | K 2 Mg [SO 4 ] 2 • 6H 2 O |
|
Mineral class (and possibly department) |
Sulfates (including selenates, tellurates, chromates, molybdates, and tungstates) |
|
System no. to Strunz and to Dana |
7.CC.60 ( 8th edition : VI / C.19) 03/29/06/01 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | P 2 1 / a (No. 14, position 3) |
| Lattice parameters |
a = 9.07 Å ; b = 12.21 Å; c = 6.11 Å β = 104.8 ° |
| Frequent crystal faces | {001}, {010}, {100}, {110}, {011}, { 2 01}, { 1 11} |
| Physical Properties | |
| Mohs hardness | 2.5 |
| Density (g / cm 3 ) | measured on the synthetic crystal: 2.028; calculated: 2.031 |
| Cleavage | completely after { 2 01} |
| colour | colorless, white, gray, reddish, yellowish |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss |
| radioactivity | hardly measurable |
| Crystal optics | |
| Refractive indices |
n α = 1.461 n β = 1.463 n γ = 1.476 |
| Birefringence | δ = 0.015 |
| Optical character | biaxial positive |
| Axis angle | 2V = 47 ° (measured), 46 ° (calculated) |
| Other properties | |
| Chemical behavior | soluble in cold water |
| Special features | bitter taste |
Picromerite (synonym: Schönite ) is a rarely occurring mineral from the mineral class of "sulfates (including selenates, tellurates, chromates, molybdates and tungstates)". It crystallizes in the monoclinic crystal system with the chemical composition of K 2 Mg [SO 4 ] 2 · 6H 2 O, making it chemically seen a water-containing potassium - magnesium - sulphate .
Picromerite is mostly found in the form of massive mineral aggregates and crusty coatings on other salts, but also develops short prismatic crystals , which in rare cases can reach a size of about five centimeters. In its pure form, picromerite is colorless and transparent. However, due to multiple light refraction due to lattice construction defects or polycrystalline training, it can also be translucent white and, due to foreign admixtures, take on a gray, reddish or yellowish color.
Etymology and history
Picromerite was first discovered on the Vesuvius volcano in the Italian region of Campania and described by Arcangelo Scacchi in 1855 . He named the mineral after the Greek words πικρός [pikros] for 'bitter' and μέρος [meros] for 'part' or 'part' in reference to its bitter taste and its chemical relationship to the Epsomite known as Epsom salt (Mg [SO 4 ] · 7H 2 O).
classification
In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the picromerite belonged to the mineral class of "sulfates, chromates, molybdates, tungstates" (as well as some selenates and tellurates) and there to the department of "water-containing sulfates, without foreign anions " , where he named the "Pikromeritgruppe" with the system no. VI / C.19 and the other members Boussingaultit , Cyanochroit , Mohrit and Nickelboussingaultit formed.
The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the International Mineralogical Association (IMA), also classifies picromerite in the category of "sulfates (selenates, etc.) without further 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 medium-sized and large cations", where it also forms the "picromerite group" together with Boussingaultite, cyanochroit, mohrite and nickelboussingaultite with the system no. 7.CC.60 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns picromerite to the class of "sulphates, chromates and molybdates" (including selenates, tellurates, selenites, tellurites and sulphites) and there in the category of "water-containing acids and sulphates" . Here it can only be found together with cyanochroite in the unnamed group 29.03.06 within the sub-section "Water-containing acids and sulfates with (A + ) 2 B (XO 4 ) 2 × x (H 2 O)".
Crystal structure
Picromerite crystallizes monoclinically in the space group P 2 1 / a (space group no. 14, position 3) with the lattice parameters a = 9.07 Å ; b = 12.21 Å; c = 6.11 Å and β = 104.8 ° as well as 2 formula units per unit cell .
properties
Picromerite samples dehydrate after some time in dry air, so they gradually give off their water of crystallization , which is recognizable in crystals by spherical, cloudy drainage zones. When the water is completely drained, picromerite changes into the mineral langbeinite (K 2 Mg 2 [SO 4 ] 3 ).
Education and Locations
At its type locality on Vesuvius, picromerite was discovered as a sublimation product of volcanic gases in active fumaroles , although this form of mineral formation in picromerite is relatively rare. It occurs more frequently as secondary mineral formation in potash salts in deposits of marine evaporites . It can also be found in sulphate-rich, hydrothermally formed ore deposits. Anhydrite , epsomite , halite , hohmannite , kainite , metasideronatrite and metavoltine can occur as accompanying minerals depending on the location .
As a rare mineral formation, picromerite could only be detected at a few sites. So far (as of 2015) around 40 sites are known worldwide. In addition to Vesuvius, the mineral occurs in Italy on I Mondei (Ca 'Mondei) near Montescheno (Piedmont) and in La Grotta Cutrona on Etna (Sicily).
In Germany, Pikromerit was able to work in various potash salt mines in the Werra Valley and near Neuhof in Hesse; at Hänigsen , Wathlingen , Lehrte and Astfeld in Lower Saxony, at Morsleben and in the potash deposits near Staßfurt in Saxony-Anhalt as well as in the Lichtenberg tailings pile near Ronneburg and in the Roßleben potash plant in Thuringia.
In Austria, picromerite was found in the Halltal salt mine in Tyrol, as well as on the Bad Ischler Salzberg and in the Hallstatt salt mine in Upper Austria.
In China , picromerite was found on salt lakes.
Other locations include Chile, the Czech Republic, Kazakhstan, Poland, Iran, Ukraine, the United Kingdom (UK) and the United States of America.
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. 610 (first edition: 1891, as Schönit).
Web links
Individual evidence
- ↑ a b c d 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. 390 .
- ↑ a b c d Picromerite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF 66.3 kB )
- ↑ Webmineral - Picromerite
- ↑ a b c d e Mindat - Picromerite
- ^ A b Helmut Schrätze, Karl-Ludwig Weiner: Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin / New York 1981, ISBN 3-11-006823-0 , p. 591 .
- ^ Arcangelo Scacchi : Memoria sullo incendio vesuviano del mese di Maggio. Nobile, Napoli 1855, p. 191
- ↑ Mindat - Number of localities for Picromerite
- ↑ Find location list for picromerite at the Mineralienatlas and at Mindat