Melanterite
- Ferrous sulphate
Melanterite, also known as green vitriol, is a rather frequently occurring mineral from the mineral class of " sulfates ( and Related ) ". It crystallizes in the monoclinic crystal system with the chemical composition Fe [ SO4 ] · 7H2O, is therefore a hydrous iron (II ) sulfate.
With a Mohs hardness of 2 melanterite belongs to the soft minerals, which can be similar to the reference mineral gypsum scratched with a fingernail. In nature it is found mostly in the form of moderate to powdery or fibrous to acicular mineral aggregates, concretions and stalactites and crusty coatings or efflorescence. He rarely also forms tabular, prismatic crystals or pseudooctahedral with glass glossy surfaces.
Special Features
Fresh and very pure state melanterite is of light blue color that by partial oxidation in iron (III ) sulfate is a light green color. Depending on the degree of weathering the mineral comes in nature in different mixed colors from greenish blue to bluish green. However, his stroke color is always white.
On dry air dehydrates melanterite, so loses some of its water of crystallization. By heating this process can be reinforced until it finally merges with the simple hydrous and yellowish to colorless sulfate mineral Szomolnokit (Fe [ SO4 ] · H2O).
Melanterite is readily soluble in water, sweet- tasting, but comes at the same time astringent ( astringent ).
Etymology and history
Sulphate of iron was known in the Middle Ages and was mixed among other various remedies and used in impure, containing copper form a so-called Copper Water for writing ink.
His final name melanterite received the mineral in 1850 by Wilhelm Ritter von Haidinger, the μελαντηρία it after the Greek word named for vitriol.
Classification
Already in the outdated, but partly still in use 8th edition of the mineral classification by Strunz was one of melanterite to the mineral class of " sulfates, selenates, tellurates, chromates, molybdates, tungstates " and then to the Department of " water -containing sulfates without foreign anions ," where he as the namesake of " Melanteritgruppe " with the system no. Formed VI/C.06 and the other members Bieberit, Boothit, Mallardit and Zinkmelanterit.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the melanterite also in the department of " sulfates ( selenates, etc. ) without additional anions, with H2O" one. However, this is further divided according to the relative size of the cations involved, so that the mineral is "With only medium-sized cations " to find according to its composition in the subdivision where it also as a name the " Melanteritgruppe " with the system no. 7.CB.35 and the other members Alpersit, Bieberit, Boothit, Mallardit and zinc melanterite forms.
The mostly commonly used in English-speaking classification of minerals according to Dana assigns the melanterite in the class of " sulfates, chromates and molybdates " and there in the department of " water -containing acids and sulfates " one. Here he is in the eponymous " Melanteritgruppe ( heptahydrate, monoclinic: P21 / c) " with the system no. Find 29.06.10 and the other members Alpersit, Bieberit, Boothit, Mallardit and Zinkmelanterit within the sub-division of " water -containing acids and sulfates with AXO4 × x (H2O) ".
Modifications and varieties
So far, two varieties are known: The copper-containing Pisanit and magnesium-containing Kirovit.
Education and Locations
Melanterite is a secondary mineral and usually formed as an oxidation product of primary iron sulphides such as pyrite, marcasite and pyrrhotite. Often he finds himself, therefore, as a neoplasm in mines. However, in rare cases, it may also arise directly as a sublimate from volcanic gases.
As a rather rare mineral formation can melanterite at different sites may sometimes be abundant indeed, but overall he is not widespread. Total so far (as of 2013) are some 870 localities known as.
In Germany, found the mineral in several places in the Black Forest and the communities Nussloch, Bruchsal and Schriesheim in Baden- Württemberg; in the Bavarian Forest, near Lichtenberg and forest Assen in Bavaria; at Messel, Richelsdorf and im Taunus in Hesse; at the Rammelsberg in Saxony; in many places and pits in North Rhine -Westphalia, such as, among others, in the Eifel region (up to Rhineland- Palatinate ), in the Ruhr and Sauerland; at Königsberg, in Rockhausen and in the Westerwald Rhineland -Palatinate; several places in the community and at Nonnweiler Dudweiler in Saarbrücken; in the Harz in Saxony -Anhalt; at several locations in the Erzgebirge and Potschappel, in Upper Lusatia in Saxony and in Oelsnitz and in Gera, Saalfeld / Saale and Lehesten in Thuringia.
In Austria, the mineral occurred in several parts of Carinthia, Salzburg and Styria as well as Gloggnitz in Lower Austria and Tyrol's Inn Valley.
In Switzerland, they found melanterite in the Schaffhausen community Thayngen, in Maderanertal ( Golzern ) in the canton of Uri, in the salt mine at Bex in Canton Vaud, and at several locations in the canton of Valais.
Noteworthy due to exceptional Melanteritfunde among other Chvaletice in the Czech Republic, where stalactites were discovered by up to 20 cm in length. Even longer stalactites (up to 2 m) as well as large crusts were found in the " Aljustrel Mine" in Portugal. Especially nice developed crystals of up to 2 cm in size were from the mines of the mining town of Bisbee, Arizona and the " Boyd Mine" in Ducktown in Polk County, Tennessee in the United States revealed.
Other localities lie in Argentina, Australia, Belgium, Bolivia, Bulgaria, Chile, China, Denmark, France, Greece, Hungary, Iran, Italy, Japan, Canada, Kyrgyzstan, Kosovo, Morocco, Macedonia, Mexico, Namibia, the Netherlands, on New Zealand, Norway, Poland, Portugal, Romania, Russia, Sweden, Slovakia, Slovenia, Spain, South Africa, Taiwan, Turkmenistan, Ukraine, the United Kingdom ( UK) and in the United States of America (USA).
Crystal structure
Melanterite crystallizes in the monoclinic space group P21 / c ( Raumgruppen-Nr. 14) with the lattice parameters a = 14.07 Å; b = 6.50 Å; c = 11.04 Å and β = 105.6 °, and four formula units per unit cell.