Almandine
- Eisentongranat
- Iron - alumina garnet
Almandine, also known as Eisentongranat or iron - alumina garnet, is a mineral belonging to the group of garnets within the mineral class of " silicates and Germanates ". It crystallizes in the cubic crystal system with the idealized composition Fe3Al2 [ SiO4 ] 3, is so chemically seen an iron-aluminum silicate, which structurally belongs to the island silicates.
Almandine is the iron analogue of spessartine ( Mn3Al2 [ SiO4 ] 3) and pyrope ( Mg3Al2 [ SiO4 ] 3) and forms with them a series of solid solutions, the so-called " Pyralspit series". Since almandine also forms with grossular ( Ca3Al2 [ SiO4 ] 3) mixed crystals, has natural almandine to a correspondingly wide range of composition with greater or lesser depending on the conditions of formation proportions of manganese, magnesium and calcium. In addition, more rarely, scandium, yttrium, europium, ytterbium, hafnium, thorium and uranium can still traces of sodium, potassium, chromium and vanadium, may be present.
The mineral is transparent to translucent and typically developed rhombic dodecahedron or Ikositetraeder as well as combinations of these crystal forms, which act almost spherical. Also often found are granular to massive mineral aggregates. In general Almandinkristalle can reach a size of several centimeters in diameter. However, it also became known Giant crystals up to one meter in diameter. The color of almandine usually varies from dark red and red-violet, but can also be brownish-red to almost black.
Almandine is the world's most common and often comes in garnet abrasive qualities worthy ago with a strong, glass-like sheen, which makes it a highly popular gemstone.
Etymology and history
Almandine was already Pliny the Elder (ca. 23-79 AD). Known under the name Alabandicus and generally belonged to the " carbuncles " ( Carbunculus ), that is red gems. It was named after the ancient city of Alabanda in Caria (Asia Minor, in Turkey's Aydın Province today ), where the stone said to have been edited. Therefore Alabanda is also regarded as type locality for almandine.
In the Middle Ages, various modifications of the name were in circulation alabandina as, among other things, Alabandra and Alabanda. Albertus Magnus ( 1200-1280 to ) introduced the term Alamandina, which corresponded to almost its present form.
In 1800, the name of Dietrich Ludwig Gustav Karsten almandine ( 1768-1810 ) was eventually finalized on the Eisentongranat.
Curiously, the 1784 first described and especially like manganese sulfide Alabandin was also named after the Turkish village of Alabanda, although it has not yet been detected there.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the almandine belonged to the department of " island silicates ( nesosilicates ) ", where he, together with andradite, Calderit, Goldmanit, grossular, Henritermierit, Hibschite, Holtstamit, Hydrougrandit, katoite Kimzeyit, Knorringit, majorite, Morimotoit, pyrope, Schorlomit, Spessartine, Uvarovite, wadalite, Yamatoit the " garnet " with the system no. VIII/A.08 formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the almandine also in the department of " island silicates ( nesosilicates ) ". However, this is further subdivided according to the possible presence of other anions and the coordination of the cations involved, so that the mineral according to its composition in the subsection " island silicates without other anions; Cations can be found in oktahedraler and usually greater coordination, " where, together with andradite, Blythit, Calderit, Goldmanit, grossular, Henritermierit, Hibschite, Holtstamit, Hydroandradit, katoite, Kimzeyit, Knorringit, majorite, Morimotoit, pyrope, Schorlomit, Skiagit Spessartine, Uvarovite and wadalite the " garnet " with the system no. 9.AD.25 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the almandine in the department of " island silicate minerals ." Here he is with pyrope, spessartine, Knorringit, majorite and Calderit in the " garnet group ( Pyralspit series) " with the system no. Find: " SiO4 groups with cations and > coordination island silicates " 51.04.03a within the subdivision.
Varieties and modifications
Rhodolite, commonly known as Oriental garnets are pink to red-purple almandine varieties, strictly speaking, almandine - pyrope solid solutions with a mixing ratio of magnesium: 1 and a density of ≈ 3.84 g / cm ³: Iron ≈ 2. Known occurrences for Rhodolite include Brazil, India, Kenya, Madagascar, Mexico, Zambia and Tanzania.
Also the Malaya garnet is a almandine pyrope solid solution with the same find areas such as Rhodolite, but rather of reddish orange. It was named after the Swahili word for malaya " outside the family standing ."
Education and Locations
Almandine is a characteristic mineral of metamorphic rocks such as, among others, mica schist, amphibolite, granulite and gneiss. Almandinreiche grenade can also form in igneous rocks such as granite and granite pegmatite. The crystals are normally embedded in the parent rock ( blasts ) and separated from other almandine crystals. Grenade with the previously highest known Alma things holding of 86.7 % (as of 1995) was found in Kayove in Rwanda, but also in Germany occurred already almandinreiche crystals of around 76 %, so any of these ground corn.
As a frequent mineral formation almandine is found in many localities, where so far (as of 2014) are considered to be known around 2200 localities. Is accompanied almandine among other things, various amphiboles, chlorite, plagioclase and pyroxene and of andalusite, biotite, cordierite, hematite, kyanite, sillimanite and staurolite.
Apart from its type locality Alabanda the mineral in Turkey only occurred so far in the garnet amphibolites near Çamlıca on the Asian side of Istanbul.
In Germany almandine could at several locations in the Black Forest ( Freiburg im Breisgau, Clara mine in Oberwolfach ) in Baden- Württemberg, in many places in Bavaria ( Bavarian Forest, Upper Palatinate Forest, Spessart ) in Ruhlsdorf / Eberswalde- Finow in Brandenburg, in some places in the Odenwald ( Erlenbach, lime rock), near Bad Harzburg in Lower Saxony, near Bad Doberan in Mecklenburg- Vorpommern, with pearls Hardt and at the Drachenfels ( King Winter ) in North Rhine -Westphalia, in many places in the Eifel region of Rhineland -Palatinate, in the pit " God reward" for melting in the Saarland, in the quarry Diethensdorf and Penig as well as in many places in the Ore Mountains in Saxony and in some places in Schleswig- Holstein ( Barmstedt, Kiel, Schleswig, Travemünde ) are found.
In Austria, the mineral found so far mainly in Carinthia in the Gurktaler Alps and the Saualpe, in the Kor from Carinthia to Styria and in the Lower Tauern, but also in several places in Lower Austria (Wachau, Waldviertel ), Salzburg ( Hohe Tauern ), in the Tyrolean Zillertal valley and Gurgler and at some points Fund in Upper Austria and Vorarlberg.
In Switzerland Almandinfunde have been known so far only from a few locations in the cantons of Ticino ( Gotthard massif) and Wallis ( Binn valley ).
Known due to exceptional Almandinfunde include the Ishikawa - pegmatites in Fukushima Prefecture on the island of Honshu and Japanese Shengus on Haramosh in Pakistan, where well-trained Almandinkristalle were discovered by up to 15 centimeters in diameter. Up to 5 inches large crystals were found among other things, in the gneisses and mica schists at Fort Wrangell in Alaska and at Bodø in Norway. Also in Italy, or South Tyrol Almandine were found of considerable size to the grenade Kogel in Seebertal.
Other localities lie include Afghanistan, Egypt, Ethiopia, Algeria, Angola, Antarctica, Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Burkina Faso, Chile, China, the Democratic Republic of the Congo, Finland, France, French Guyana, Greece, Greenland, Guatemala, India, Ireland, Israel, Canada, Colombia, Korea, Madagascar, Malawi, Mexico, Mongolia, Myanmar, Namibia, Nepal, New Caledonia, New Zealand, Norway, Poland, Portugal, Romania, Russia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Slovenia, Spain, Sri Lanka, South Africa, Taiwan, Tajikistan, Thailand, Czech Republic, Ukraine, Hungary, Uzbekistan, the United Kingdom ( UK) and the United States of America (USA).
Crystal structure
Almandine crystallizes in the space group Ia3d cubic ( Raumgruppen-Nr. 230 ) with the lattice parameters a = 11.53 Å, and eight formula units per unit cell.
Use
Almandine is used as most of the other minerals of the garnet family especially as a gemstone, which can be ground depending on the purity and clarity in facet shape or Cabochonen. Less noble that is too dark and opaque varieties can also be used as an abrasive.
Likelihood of confusion, especially with the various Granatvarietäten due to the predominant formation of solid solutions between the end members. In addition, almandine but can also be confused with ruby, spinel and red tourmalines. Due to the difficult distinction the various garnet names are now widely used in the gem trade as a color name, with almandine and rhodolite represent the pink to violet grenade.
The largest known and cut almandine gemstone is a cabochon 175 ct, which is preserved in the Smithsonian Institution in Washington, DC.