Uvarovite

The mineral Uvarovite is a rarely occurring island silicate from the garnet group and has the chemical composition Ca3Cr2 [ SiO4 ] 3 Uvarovite crystallizes in the cubic crystal system and usually develops small, well- shaped crystals up completely, but also granular aggregates. Due to mixed crystal formation and foreign admixtures of color varies from dark - on emerald - green to brown. Depending on the purity, crystal defects and / or the amount of inclusions, crystals glass - to -fat shiny and be transparent to opaque.

Special Features

Uvarovite belongs to the so-called theoretical end members of a mixed batch and forms with grossular and andradite uninterrupted Ugrandit - mixed batch. With another gapless mixed batch ( Pyralspit series), consisting of the end-members pyrope, almandine and spessartine, Uvarovite can form limited solid solutions. Pure end-members of a mixed batch, however, are found only rarely in nature. They can be produced synthetically, though, but then we usually only of minor importance as objects of investigation. So almost always is the case of natural objects found in the garnet group mixed crystals, which are named after this at a fraction of more than 50% of the end-members.

For the same reason, the physical and optical values ​​vary according to the composition of the relevant mineral or, strictly speaking, the mixed crystal. For example, the scale of Moh's hardness ranging from 6.5 to 7 when Uvarovite (according to other sources 7 to 7.5) and the density of 3.4 to 3.8 g / cm ³.

Etymology and history

Was named the mineral after the Russian count, mineral collector and President of the Imperial Academy of Sciences Sergei Semenovich Uvarov. The first find was made in the deposit Biserskoje ( Biser ) in the Middle Urals.

The earliest scientific description of Uvarovite dates from the year 1832 by the Swiss- Russian chemist Germain Henri Hess.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Uvarovite belonged to the mineral class of " silicates and Germanates " and then to the Department of " island silicates ( nesosilicates ) ", where he, together with andradite, Goldmanit and Grossular the " Ugrandit series " within 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 Uvarovite into the class of " silicates and Germanates " and then in the Department of the " island silicates ( nesosilicates ) ". This division, however, 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 and its construction in the subsection " island silicates without additional 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 Spessartine, Skiagit 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 Uvarovite in the class of " silicates and Germanates " and then in the Department of the " island of silicate minerals " one. Here he is as together with andradite, grossular, and Goldmanit Yamatoit in the " garnet group ( Ugrandit series) " with the system no. Find: " SiO4 groups with cations and > coordination island silicates " 51.04.03b within the subdivision of.

Education and Locations

Uvarovite is likely to form in metamorphic or hydrothermal contexts, rare in igneous rocks such as pegmatites. The mineral needs to the emergence of increased chromium content and an ultrabasic environment, that is a particularly low content of silica (SiO2). These conditions can be found among others in chromithaltigen serpentinites and skarns.

As a well-known localities in Russia are primarily the mines in the Perm region in the south of Biser Saranowskoje and Teplaja Gora in Sarany where Uwarowitkristalle of up to eight millimeters were found. In Sverdlovsk Oblast, among other Verch - Nejvinskij, Alapaewsk, Stary Itkul'skoje and Iremel'skoje be mentioned.

Crystals of up to two centimeters and particularly large crystal aggregates come from the Finnish Outokumpu deposit.

Other localities include Assosa in the province Wollega in Ethiopia; the Chromitlagerstätten in the southeast part of New South Wales and Tasmania in Australia; Xinjiang in the People's Republic of China; Mokkivaara and Pohjois- Karjala in Finland; Lombardy and Val Malenco in Italy; the prefectures Kōchi and Ehime in Japan; Quebec in Canada; Moa - Baracoa massif in as inclusions in serpentinite in the province of Guantánamo in Cuba; Nordland, Røros, Grua and Velfjord in Norway; Styria and Tyrol in Austria; Serpentinitmassiv in the region around Sobotka in Poland; Eastern Anatolia and Cape Dağları in Turkey; as well as Alaska, Arizona, several regions in California, Colorado, Maine, Michigan, Nevada, New Mexico, New York, Oregon, Pennsylvania, Texas, Vermont and Washington in the United States.

Crystal structure

Uvarovite crystallizes in the cubic system, space group Ia3d ( Raumgruppen-Nr. 230) mitt to the lattice parameter a = 12.00 Å, and eight formula units per unit cell. The crystals show isometric forms. The cations lie in oktahedraler and cubic configuration [8 6 ].

Use as a gemstone

Uvarovite is mainly processed into semi-precious stones. Jewels, which Uvarovite was processed since the Merovingian period are detectable. On the occurrence in the Ural based the first scientific description of Uvarovite. The best crystals from this deposit was exploited to Preziosenherstellung at the imperial court. In Russian history, one speaks of the " imperial stone " because the inclination of the Empress Catherine II is known for this mineral.

Uvarovite is sometimes confused with the equally rare and somewhat brighter green Demantoid mineral ( Fe3 Cr3 ), which is also a member of the garnet group. Another color possibility of confusion exists with the grossularite variety Tsavorite and with emerald.