Zoisite

Zoisite (also Saualpit ) is a mineral from the mineral class of " silicates and Germanates ", which may be abundant in various localities in part, but overall is not widespread. It crystallizes in the orthorhombic crystal system with the chemical composition Ca2Al3 [O | OH | SiO4 | Si2O7 ] and usually develops transparent to translucent crystals up to 10 cm in length and prismatic habit, often striated lengthwise. Also massive, granular, or radial- mineral aggregates are known.

With a Mohs hardness 6-7 zoisite is one of the medium-hard to hard minerals. To carve it, it needs at least a steel file, but he himself is able to carve simple window glass.

Reiner zoisite is colorless, but it can be by various admixtures of gray to yellow, green, pink to red or blue to violet color. The stroke color of Zoisits but you will always know. Undamaged, smooth crystal faces have a vibrant, glass-like luster, cleavage surfaces shimmering mother of pearl, however, rather similar.

Zoisite is known primarily for its gem varieties Tanzanite (blue violet) and Thulit ( pink ).

Special Features

Zoisite has similar cordierite on a clearly visible pleochroism, which can be very strong, especially in the variety Tanzanite:

Zoisite is heat sensitive and reacts to it with color change, which is used, among other things, by the usually found in the mines, gray-brown zoisite is converted by firing at about 550 ° C in the coveted blue tanzanite.

Etymology and history

Was first discovered the mineral from a mineral dealer (presumably Simon Preschern ) on the so-called " Prickler stop", a ridge between Speikkogel and Ladinger pointed in the Austrian state of Carinthia, who first described the Fund after its type locality as Saualpit and the entrepreneur and scientist Sigmund Zois Freiherr von Edelstein (1747-1819) handed, who had supported the expedition of the mineral dealer.

However Zois suspected that it was a question of a new, previously unknown mineral type, informing next to the mineralogist Abraham Gottlob Werner (1749-1817), Martin Heinrich Klaproth (1743-1817) at this discovery, which can confirm his suspicions. Werner gave the new mineral in 1805 in honor of the Zois today recognized name zoisite.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the epidote belonged to the mineral class of " silicates and Germanates " and then to the Department of " group silicates ( Sorosilikate ) ", where he, together with allanite - (Ce), allanite - (La), allanite - (Y), Dissakisit - (Ce), Dissakisit - (La), Dollaseit - (Ce), epidote - (Pb), epidote, Ferriallanit - (Ce), Gatelit - (Ce), Khristovit - (Ce), clinozoisite, clinozoisite - ( Sr), Manganiandrosit - (Ce), Manganiandrosit - (La), Manganipiemontit - ( Sr), Mukhinit, piemontite, piemontite - ( Sr), Uedait - (Ce), Vanadoandrosit - (Ce ) and Västmanlandit - (Ce ) for " Epidotgruppe " belonged.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the epidote also included in the category of " silicates and Germanates " and there in the department of " group silicates ( Sorosilikate ) ". This division, however, is further subdivided by the type of group formation of silicate complexes and the coordination of the cations, so that the mineral according to its composition and structure in the sub-division of " group silicates with mixed SiO4 and Si2O7 groups; Cations can be found in octahedral coordination and greater, "where is the unnamed group 9.BG.10 the only member.

The mainly common in English-speaking classification of minerals according to Dana assigns the epidote in the class of " silicates and Germanates " there, however, in the already fine divided department of " group silicates: Insular, Mixed, individual and larger tetrahedral groups." Here he is the only member of the " Epidotgruppe ( zoisite - subgroup ) " with the system no. 58.02.01b within the sub-division of " group silicates: Insular, Mixed, individual and larger groups with cations in tetrahedral and higher coordination; Single and double groups (n = 1,2) to find ".

Modifications and varieties

From zoisite several varieties are known:

• Tanzanite - blue to blue-violet, first found in 1967 in Tanzania
• Thulit - red by admixtures of manganese. Partial but it is in the described Thuliten to varieties of clinozoisite.

Anyolite (h ) (also Zoisitfels ), however, is an aggregate or better rock of green zoisite, red, opaque ruby and often also with inclusions of black hornblende ( amphibole minerals of ).

Education and Locations

Zoisite formed by metamorphism in calcium - rich rocks such as pyroxene gneiss and amphibolite, but also by contact metamorphism in marble. Accompanying minerals include various garnets and hornblende, albite, biotite, calcite, and quartz.

Overall, zoisite so far (as of 2011) are detected at around 750 localities. Apart from its type locality " Prickler stop" in the Saualpe the mineral in Austria nor in mountain hut, the Gurktaler Alps, near Moosburg, the Milstätter lake and Winklern in Carinthia was; at Bader village in Burgenland; at Dunkelsteinerwald and in the Waldviertel in Lower Austria; in the Hohe Tauern Carinthia to Salzburg, Kitzbühel Alps; at the Kor from Carinthia to Styria; at the Packalpe and exchange in Styria and in Virgen, Inn, Ötztal and Zillertal in Tyrol.

In Germany Zoisite was among others Bötzingen in Baden -Württemberg; at several locations in Franconia, Lower Bavaria and the Upper Palatinate in Bavaria; in the Hessian Odenwald; in Lower Saxony Harz; found in the Eifel region of Rhineland -Palatinate and in the Saxon Erzgebirge.

In Switzerland, the mineral previously occurred in the Valle Maggia and Verzasca Valley in Ticino and Valais in the Binn Valley, near Brig, Martigny and Zermatt.

Other localities are Antarctica, Australia, Belgium, Brazil, Chile, China, Finland, France, Greece, Greenland, Guatemala, India, Ireland, Italy, Jamaica, Japan, Kazakhstan, North and South Korea, Madagascar, Mexico, New Zealand, Norway, Oman, Pakistan, Paraguay, Poland, Romania, Russia, Sweden, Zimbabwe, Slovakia, Slovenia, Spain, South Africa, Taiwan, Tanzania, Turkey, Ukraine, the United Kingdom ( UK) and the United States of America (USA).

Crystal structure

Zoisite crystallized dimorphic with clinozoisite in the orthorhombic crystal system, space group ( Raumgruppen-Nr. 62) with the lattice parameters a = 16.19 Å; b = 5.55 Å and c = 10.03 Å and four formula units per unit cell.

Use as a gemstone

Although known and sought after as a precious stone are especially rare varieties Tanzanite and Thulit, but also differently colored varieties may in good, that is clear and inclusion- poor quality beautiful jewelry stones are cut.

Since the mineral, however, is sensitive to excessive and uneven heating, drum and repair work must be carried out with appropriate care. Even the touch of the stone the brazing flame can eg lead to blistering and let it swell.