Spessartine

• Manganese - alumina garnet

Spessartine, also called manganese - alumina garnet, is a commonly occurring mineral from the group of garnets within the mineral class of " silicates and Germanates ". It crystallizes in the cubic crystal system with the idealized composition Mn3Al2 [ SiO4 ] 3, is so chemically seen a manganese aluminum silicate, which structurally belongs to the island silicates.

Spessartine is the manganese analogue of almandine ( Fe3Al2 [ SiO4 ] 3) and pyrope ( Mg3Al2 [ SiO4 ] 3) and forms with them a series of solid solutions, the so-called " Pyralspit series". Since Spessartin also with the other garnet mineral andradite ( Ca3Fe23 [ SiO4 ] 3) Calderit ( Mn3Fe23 [ SiO4 ] 3) and grossular ( Ca3Al2 [ SiO4 ] 3) mixed crystals forms Spessartin shows a correspondingly wide range of composition depending on the formation conditions greater or lesser amounts of iron, magnesium and calcium.

The mineral is transparent to translucent and develops typically rhombic dodecahedron, or more frequently Ikositetraeder as well as combinations of these crystal forms, which act almost spherical and can reach up to 10 centimeters in diameter. In addition, it also occurs in coarse or massive aggregates. The color of Spessartite usually varies between orange and yellow, but can also be brown-red on dark red to black.

Etymology and history

Spessartin 1832 was named by François Sulpice Beudant after Spessart, because in this mountain range was the Stengerts near Aschaffenburg one of the most historically important sites for Spessartin.

As a type locality applies the Sommer'sche quarry at Wendelsberg near Haibach in the Lower Franconian district of Aschaffenburg. Since 1985, no longer approached, but abandoned quarry and the surrounding area is protected as a natural monument of botanical reasons. Collecting is allowed there only in accordance with Exemption to Excursion, research and teaching purposes.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Spessartin belonged to the department of " island silicates ( nesosilicates ) " where he, along with almandine, andradite, Calderit, Goldmanit, grossular, Henritermierit, Hibschite, Holtstamit, Hydrougrandit katoite, Kimzeyit, Knorringit, majorite, Morimotoit, pyrope, Schorlomit, 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 Spessartin 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, along with almandine, andradite, Blythit, Calderit, Goldmanit, grossular, Henritermierit, Hibschite, Holtstamit, Hydroandradit, katoite, Kimzeyit, Knorringit, majorite, Morimotoit, pyrope, Schorlomit Skiagit, 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 Spessartin in the department of " island silicate minerals ." Here he is with pyrope, almandine, 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

• As a Mandarin garnet. or Kunene Spessartine. is called a bright orange variety of spessartine from Marie River, a tributary of the Kunene River in Namibia.
• Umbalith. is after the Umba Valley in Tanzania named, orange spessartine solid solution with proportions of almandine, grossular and pyrope. See occasional, additional third-party additions of vanadium and chromium can cause a process known as alexandrite effect color change from blue-green to purple.
• Spandit. is a historical, not more common name for a spessartine - andradite solid solution. The name was proposed in 1909 by Lewis Leigh Fermor ( 1880-1954 ), but not prevailed.

Spessartite ( after H. Rosenbusch, 1896), however, is not synonymous with Spessartine, as sometimes erroneously to read, but a belonging to the lamprophyres, magmatic gangue of Kersantit - Spessartite - series of dark gray to black in color.

Education and Locations

Spessartine is formed in manganese-rich than Nebengemengteil granites and granite pegmatites. However, it can also be caused by regional metamorphism in manganese-rich sediments such as in the " Wetzschiefern " of the Ardennes. Accompanying minerals occur among others albite and other alkali feldspars, Alleghanyite, apatite, beryl, bixbyite, galaxite, muscovite, pseudobrookite, Pyroxmangit, quartz, rhodonite, tephroite, topaz, tourmaline.

As a frequent mineral formation Spessartin is found in many localities, where so far (as of 2012) around 1000 localities as are known. Apart from its type locality Wendelsberg the mineral nor entered into Germany, among others, in many other places in the Bavarian Forest ( Arnbruck, Zwiesel ), in the quarry terminal stream near Schweighof / Badenweiler in Baden- Württemberg, near Bad Harzburg in Lower Saxony, at several places in the Eifel region of Rhineland -Palatinate and resin between Saxony -Anhalt and Thuringia and at Schneeberg, Königshain and Döbschütz in Saxony.

In Austria has been able spessartine be found especially in Carinthia and Styria ( Friesach - hut mountain, Koralpe ), but also in Lower Austria's Waldviertel, the Hohe Tauern in Salzburg and East Tyrol.

In Switzerland, the mineral is found so far only in a few places in the cantons of Graubünden and Valais.

Other localities lie include Afghanistan, Egypt, Antarctica, Argentina, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Finland, France, Ghana, Greece, India, Italy, Japan, Kazakhstan, Kyrgyzstan, Korea, Madagascar, Morocco, Mozambique, Myanmar, Namibia, New Zealand, Nigeria, Norway, Pakistan, Peru, Poland, Portugal, Romania, Russia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Spain, Sri Lanka, South Africa, Taiwan, Tanzania, Thailand, Turkey, Ukraine, the United Kingdom ( UK) and the United States of America (USA).

Spessartite ( orange ) and lepidolite from Italy

Spessartine (dark red), aquamarine and schorl ( black tourmaline) on albite from Pakistan

Dark Red Spessartine as inclusion in almost colorless beryl from Pakistan

Wine Red Spessartine of unusual form and size (7.5 x 6.5 x 3 cm) from Minas Gerais, Brazil

Crystal structure

Spessartin crystallizes in the space group Ia3d cubic ( Raumgruppen-Nr. 230 ) with the lattice parameters a = 11.62 Å, and eight formula units per unit cell.

Use

Like most other abrasive worthy garnet varieties will also Spessartin mainly as a gemstone use. Depending on the color form, it can be confused with andalusite, chrysoberyl, opal, Hessonite, titanite or topaz.

Due to the variety of colors, due to the extensive formation of mixed crystals of the grenade one is now gone in the gem trade to not assign the grenade after its often difficult to quantify, chemical composition, but according to their respective shade the individual garnet species which respectively serve only as color names. As Spessartin or alternatively as grossular therefore the yellow to orange garnets are called.