Polyhalite
Polyhalite is a rarely occurring mineral from the mineral class of " sulfates ". It crystallizes in the triclinic crystal system with the chemical composition K2Ca2Mg [ SO4 ] 4 • 2H2O and mostly developed acicular, platy, or columnar, prismatic crystals, as well as flaky or fibrous mineral aggregates. Through twinning polyhalite deceives often before an orthorhombic symmetry.
Special Features
Reiner polyhalite is colorless. He may also be off-white, brown, pink or red reddish-brown color by foreign admixtures, however.
The mineral dissolves in water and separates it from gypsum and possibly syngenite.
Etymology and history
Although the name suggests a similarity of polyhalite has nothing to do with the mineral halite. The ancient Greek words πολύς ( polys ) for "a lot" and ἅλας ( neck, halo) for " salt" is a reference to its complex composition with several salt-forming metals.
Was first found polyhalite 1818 Bad Ischl salt mine in Austria and described by Friedrich Stromeyer.
Classification
In the old ( 8th edition ) and new classification of minerals according to Strunz ( 9th edition ) of the polyhalite is one of the hydrous sulfates without foreign anions. The new Strunz'sche Mineral classification divided here but now more specific on the size of the cations, and the mineral is in accordance with the subsection " C. With medium -sized and large cations " to find where the unnamed group it together with Wattevilleit " 7.CC.65 forms ".
The commonly used in English-speaking classification of minerals according to Dana sorted the polyhalite also in the class of sulfates, there, however, in the department of " hydrated acids and sulfates (A ) 2Bn ( XO4 ) p • x (H2O) ," where he together with Leightonit the unnamed group " 29.4.5 " forms.
Education and Locations
Polyhalite formed mainly by sedimentary deposition in marine salt deposits, formed in rare cases, but also as a sublimate of fumaroles.
In Austria polyhalite could besides its type locality Bad Ischl salt mine still in Hallstatt in Upper Austria, Abtenau and Hallein in Salzburg, Altausee in Styria and Hall in Tirol.
In Germany polyhalite was in the Bavarian salt mine in Berchtesgaden, in Neuhof ( near Fulda ) and the Werra Valley in Hesse, near Celle, Lüneburg and Nordhorn in Lower Saxony, Saxony-Anhalt and Staßfurt in Gera and Bad Salzungen found in Thuringia.
Could Worldwide polyhalite so far (as of 2010) are detected in more than 60 localities, as, inter alia, Chile, China, France, Greece, Iran, Italy, Kazakhstan, Mexico, Netherlands, Poland, Russia, Spain, Turkey, Ukraine, Uzbekistan, United Kingdom ( UK) and the United States of America.
Crystal structure
Polyhalite crystallized in the triclinic space group ( Raumgruppen-Nr. 2) with the lattice parameters a = 6.975 Å; b = 6.984 Å; c = 8.899 Å; α = 104.01 °; β = 101.19 ° and γ = 114.10 °, and four formula units per unit cell.