Lapislazuli

Lapis lazuli, also lapis lazuli ( lapis lazuli ), lapis lazuli or shortly called Lapis is a blue shiny mineral mixture, which may be, depending on the locality of different proportions of minerals Lazurite, pyrite, calcite, and lesser admixtures of diopside, sodalite and others. As solid, naturally occurring, microscopic heterogeneous combination of minerals is one lapis lazuli, by definition, more likely to be rocks and is also sometimes referred to as such.

Etymology and history

The word comes from the Latin lapis meaning " stone ". Lazuli, genitive of Middle Latin word lazulum for " blue", derived via Arabic from Persian لاژورد / lāžward /, sky blue ' from. Synonymous terms are ultramarine, among others Azur d' Acre, azurum ultramarinum, Bleu d' Azur, lapis lazuli, Las ( z) Urstein, Lazurium, Oltremare, Orientalischblau, Outremer lapis, Pierre d' azure, ultramarine genuine, Ultramar ino / verdadero, Ultramarine natural; furthermore, according to Pliny and Theophrastus coeruleum scythium.

Lapis lazuli was already in the 3rd millennium BC, a commodity that was transported in the form of unprocessed blocks and polished jewelry beads over long distances. Of the sites in the northeastern Afghan province of Badakhshan blocks of lapis lazuli after Shahr -e Investigated were transported in what is now eastern Iran. Structural analysis revealed that it is on 1500 to 5000 meters above sea level found material in fact the same as in Shahr -e Investigated in which the valley of the River Kokcha in Badakhshan. Also Tepe Hissar in northern Iran was involved in the stone trade. In both places, workshops have been excavated from the middle of the 3rd millennium, in which, besides Lapislazulistücken also tools for editing were found: drills and blades of flint, jasper and pestle and smoother. The lapis lazuli found in Mesopotamia also came from Afghanistan. The Assyrian king Samsi - Adad I (18th century BC) mentioned under lapis lazuli precious materials which he had collected from other countries. The mineral came from here to Syria, where pearls were found for costly garments made ​​of lapis lazuli and carnelian in Ugarit, and through the mediation of the living peoples in Syria to Egypt.

Chemistry and color

First characterizations of this mineral color pigment were made ​​by Andreas Sigismund Marggraf in 1768. The first chemical analysis of the main component of lapis lazuli, the blue stone, succeeded in 1806, the French chemist Nicolas Clement from today's perspective with a already good accuracy ( Silice: 35.8 %, Alumine: 34.8 %, Soude: 23.2%, soufre: 3.1%, Chaux carbonatee: 3.1%). On this basis was in the aftermath of routes for the preparation of artificial ultramarine, which should correspond to the natural Lasurit possible, sought and developed almost simultaneously by the French chemist Jean Baptist Guimet and the German chemist Christian Gottlob Gmelin in the 1820s. Studies of natural and artificial ultramarine and related minerals sodalite, nosean and Hauyne by physical methods (from 1929 with the X-ray structure analysis) led to the realization that these substances belong to the group of aluminosilicates. Sought-after gemstones are of intense ultramarine blue color, which is on • S3 - radical anions of sulfur in the idealized formula Na6 [ Al6Si6O24 ] SxCa due ( with x > 1). Finely divided pyrite is regarded as proof of authenticity. Spots or small gold-colored pyrite veins are also appreciated, but the pyrite content should not be too large, because otherwise the color turns into an ugly green. Stones in which the calcite emerges strong, are less valuable.

The various deposits bring out shades. Tajik lapis lazuli are more navy blue, the found at Lake Baikal have blue-violet tones and particularly strong Calcitanteile on.

Education and Locations

Lapis lazuli is likely to form through metamorphosis or metasomatic operations within amphibolites, gneiss, marble, and peridotites pyroxenites. In addition, may be in addition to the minerals already mentioned, Afghanite, apatite, dolomite, Hauyne, nepheline, sulfur, tremolite and other associated.

The most common sites are in the western Hindu Kush, in the province of Badakhshan in Afghanistan. In the Afghan civil war played mastery of the Panjshir Valley, in addition to its strategic importance as a supplier of expensive Lapislazulis an important role as a source of income for the purchase of weapons. The recovery of bodies in Sar- é Sang from Kokscha Valley in Badakhshan, in the lapis lazuli is won today, was already at the time of Ancient Egypt in operation. To win the stone, he was blown up in the mine with fire: the stones was heated by local intense wood fire and then cooled with water from a sudden, after which they were cracked and could be knocked out. Today, working in Badakhshan with explosives.

Other important sites are located in Russia. Here the best color varieties of the deposit Malobystrinskoye originate at Lake Baikal. Less productive, the localities Talskoye and Sljudjanskoye proven in the Baikal region. The site on the river Slyudiyanka discovered Erich G. Laxmann in the years 1784-1785, when he at Lake Baikal operational scientific explorations on behalf of the Academy of Sciences of the Tsar. Catherine the Great sent 1787 a geological expedition to the region in order to obtain more detailed information about usable gems and minerals. As a result, samples of Lasurit arrived in St. Petersburg.

Other sites are located in Tajikistan at Ljadschwar - Dara in the Pamirs ( Gorno-Badakhshan / Schachdarja chain). In addition, localities exist in Ovalle in Chile, in Iran and in the Cascade Canyon of California and the magnet Cove, Arkansas (USA).

Use

Gem

As precious gemstone lapis lazuli or better has a history that dates back about 7,000 years. Lapis lazuli was the most precious thing the ancient Egyptians had pharaohs and their mitgaben on a journey into the afterlife (see mummy mask of Tutankhamun ). Because lapis lazuli, however, already belonged at that time the most expensive gemstones, the Egyptians were among the first who impersonated next to the turquoise and lapis among other things, with blue colored glass. In Mesopotamia, lapis lazuli was very popular with the Sumerians. Jewelry from the royal tombs in the great ziggurat at Ur, exhibited in the Museum of the Ancient Near East in Berlin and London, show the abundant use. There was demonstrable as early as 2000 BC trade relations between Egypt, Mesopotamia and the northern Afghanistan ( lapis lazuli Street, later Silk Road ).

Pigment

Lapis Lazuli played a major role as a pigment in the art. For this stone, the bright blue color was obtained, which in the Middle Ages, for example, Madonna robes were especially painted. A particularly fine example of its use as a color base material is also in the manuscript The Book of Hours of the Duke of Berry, one of the most important works of illumination. So the robes of the Duke of this color are produced on the calendar page January for example. Another notable example of the use of ground lapis lazuli as a pigment is Giotto's frescoes in Padua, where it was used for the design of Heaven. Blue shades were probably therefore rarely used in medieval painting because blue pigments such as lapis lazuli were extremely expensive and scarce and of "beyond the sea" - hence the name " ultramarine " - had to be obtained. Natural ultramarine blue was ever sought after because of its color strength and lightfastness. Therefore, the discovery of a method of preparation of this colorant was important.

Manipulation and imitation

  • Pale lapis lazuli is oiled or waxed to make it appear darker. An uneven coloring can unify with colored oil, but this is easily detectable with acetone.
  • Lapis lazuli of low quality or in small fragments is reconstructed together with synthetic resin to form larger stones.
  • Imitation of lapis lazuli are mainly produced by coloring the quartz variety jasper with Prussian blue. Thus, the so-called " German Lapis ( lapis lazuli ) " in Nunkirchen ( Wadern ) is made ​​of jasper, other names are "Swiss Lapis ", "Blue Onyx" or " Nunkirchener lapis lazuli ". By treating of such inferior gem imitations in an ultrasonic bath or with ammonia, occur on the stone surface marks that can not be removed, as the coloring pigment is replaced.
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