Hydromagnesite
- Magnesia alba or bright Magnesia
- Talkjordshydrat or Talkerdehydrat
Hydromagnesite (also magnesia alba or light magnesia ) is a rarely occurring mineral from the mineral class of " carbonates and nitrates ." It crystallizes in the monoclinic crystal system with the composition Mg 5 (CO 3 ) 4 ( OH ) 2.4 H2O, is thus seen chemically a hydrous magnesium carbonate with hydroxide ions as additional anions.
Special Features
Above about 200 ° C, decomposes to hydromagnesite release of water and carbon dioxide. What remains is magnesium oxide.
Etymology and history
Hydromagnesite was first discovered in Castle Point near Hoboken in the U.S. state of New Jersey. It was analyzed and described in 1827 by Hans Gabriel trolls - Wachtmeister ( 1782 to 1871 ) under the name magnesia alba (or Talkjordshydrat, German: Talkerdehydrat ). According to Franz von Hess Peter this designation, however, was of little importance and in the mineralogical nomenclature also inappropriate. He therefore suggested the name Hydromagnesite ago - a compound word formed from the Greek word " hydro " for water and magnesite - the diversity of magnesite emphasized as anhydrous Talkerdecarbonat.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the hydromagnesite belonged to the department of " water -containing carbonates with foreign anions ", where he. Together with Artinit the " hydromagnesite Artinit group " with the system no Formed V/E.01 and the other members Brugnatellit, Chlorartinit, Coalingit, Dypingit, Giorgiosit, indigirite and Widgiemoolthalith.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the hydromagnesite also in the department of " Carbonates with additional anions, with H2O" one. However, this is further divided according to the relative size of the cations involved, so that the mineral is found according to its composition in the subsection "With medium-sized cations " where there. Than sole namesake the " Hydromagnesitgruppe " with the System No. Forms 5.DA.05 and the other members Dypingit, Giorgiosit and Widgiemoolthalith.
The mostly commonly used in English-speaking classification of minerals according to Dana assigns the hydromagnesite in the fine already divided the department " Carbonate - hydroxyl or halogen" one. Here it is only to be found along with Widgiemoolthalith in the unnamed group 16b.07.01.
Education and Locations
Hydromagnesite is a weathering product of magnesium-containing minerals ( brucite, serpentine ) or rocks ( ultramafitite, dolomite, marble) dar. In dolomite and marble, it can be the result of hydrothermal conversion of the corresponding rocks. Hydromagnesite is typically found as encrustations or filling of fissures and cavities.
Furthermore comes in hydromagnesite ( limestone ) caves before Speläothem or as so-called moon milk. Here it is formed by magensiumreiche leachates. After calcite and aragonite, it is the most abundant mineral speleothems.
A special feature is that hydromagnesite, similar to calcite and aragonite is formed by living organisms. It is known that stromatolites under alkaline conditions (pH> 9) hydromagnesite excrete ( Salda Lake, southern Turkey ). A formation by microorganisms is also known from the Dry Lake in British Columbia.
As a rather rare mineral formation hydromagnesite may indeed be abundant in part to different sites, overall it is not very common. So far (as of 2012) are considered to be known around 280 localities. Apart from its type locality Castle Point in Hoboken in New Jersey ( a part of the Grand Canyon ) in Arizona, in many places in California, in several mines near Georgetown ( Colorado mineral occurred in the United States of America, among others, still in the " Nautiloid Canyon " ), in the " Marengo Cave " in Crawford County ( Indiana), at White Pine in Ontonagon County of Michigan, in Kings Mountain, North Carolina, Pennsylvania, at Lime Rock in Rhode Iceland and at several locations in Maryland, Nevada, New Mexico, New York, South Dakota, Tennessee, Utah, Virginia, Washington and Wisconsin.
In Germany hydromagnesite was previously at the quarry Limberg in the community Sasbach in Baden -Württemberg, in the yew grotto near Bamberg and at Zeilberg in Bavaria, on several discovery locations in Stolberg ( Rhineland ) and Hüsten ( Arnsberg ) in North Rhine -Westphalia and the Arensberg, Ettringer Bellerberg in the Eifel and in the pit Friedrichssegen the Lahn, in Rhineland -Palatinate.
In Austria, the mineral is found among others in the serpentinite quarry near Griesserhof ( Gulitzen ) near Hirt in the district Friesach - hut mountain and the book mountain near Sankt Veit an der Glan in Carinthia in Loja in the Lower Austrian town of Donau - God village, on the lower mountain in Salzburg, on Eibegggraben ( Fischbacher Alps), and in Fohnsdorf Kraubath an der Mur in Styria, on Gumpachkreuz in the back Bichler Dorfertal and the Gratlspitze in Tyrol and in the upper Traun in Upper Austria.
In Switzerland, hydromagnesite previously occurred only with Selva ( Sedrun ) in the canton of Grisons, in the salt mine at Bex in Canton Vaud and the mine Les Moulins at Saint- Luc VS in the canton of Valais.
Other localities lie among other things in Antarctica, Australia, Belgium, Bolivia, Brazil, China, France, Greece, Iran, Israel, Italy, Japan, Canada, Morocco, Mexico, Mongolia, New Zealand, Norway, Romania, Russia, Sweden, Serbia, Zimbabwe, Slovakia, Spain, South Africa, Turkey, Turkmenistan, Hungary, Uzbekistan and the United Kingdom ( UK).
Crystal structure
Hydromagnesite crystallizes in the space group P21 / c ( Raumgruppen-Nr. 14) with the lattice parameters a = 10.11 Å; b = 8.95 Å; c = 8.38 Å and 114.4 ° and β = 2 formula units per unit cell.
Use
Hydromagnesite is industrially processed together with huntite with inorganic flame retardants.
Hydromagnesite has endothermic decompose under thermal stress under release of water and carbon dioxide the property. Thereby, the flame spread when used in plastics is prevented.
As the solid Zersezungsprodukt continues to remain magnesia left. The decomposition starts with, for low fire retardant, 200 ° C, which compared to other flame retardants such as aluminum is an advantage.