Agate

When Agate is a microcrystalline variety of the mineral quartz. Striking the agate is its beautiful, streaky drawing due to the rhythmic crystallization.

Etymology and history

Theophrastus the agate was his name, when he ἀχάτης in large quantities in the river " Achates " (now called Dirillo, Carabi or Canitello ) near the local Acate was found in Sicily.

Even in early times enjoyed the agate high esteem. In ancient Egypt about 1000 BC were seal-cylinders, rings, gems and jars, agate made ​​. In the Bible, in the second book of Moses, 28, 17-20, the breastplate of the high priest, a jeweled plate described in detail. Amulets of agate should help against lightning, storm and thirst.

Beginning of the 17th century had grown already to great importance is the agate industry, a further upswing they took in the second half of the 18th century, when it began to take Agate goods first in silver, then in gilt Tombak. This Costume fausse formed especially in Oberstein and later also brought pure metal goods to market.

After 1813 it was discovered the change in color of the stones by firing, in 1819 brought a merchant from Idar -Oberstein 's acquired a Roman stone cutter mystery of the " black coloring " in the home. Since then, the dyeing agate developed very quickly and became one of the main causes of the flowering of the agate industry, which now also exotic stones, including agate from Uruguay processed. Since 1834, this material came to Idar -Oberstein and developed the agate industry in previously unknown ways, especially since plenty of South America arriving Onyxe prompted the blossoming of lapidary art in Paris and Idar. It produced mainly cameos, inlaid also, in part by high artistic value, and made with the same great shops. Exported to Africa pieces were also called Negro money.

Varieties and modifications

  • Apricot agate
  • Agate agate eyes or glasses ( spherical, eye -like drawing)
  • Banda Chat ( drawn parallel to the outer wall of the Agate almond bands of approximately equal strength )
  • Tree agate or wood agate ( agate by silica - mineralized, " petrified " wood)
  • Botswana agate
  • Enhydros or water stone ( agate almonds with remaining liquid and dried after removal from the parent rock usually made ​​soon )
  • Fortification agate ( agate bands resemble aerial photographs of ramparts )
  • Peace agate
  • Fire Agate or flame agate or agate clouds ( cloud -like bands)
  • Meat or blood agate agate
  • Honey agate
  • Coral Agate ( The name derives from the shape of the surface of agate )
  • Circle agate ( To a center concentrically or eccentrically arranged circles of the agate bands)
  • Moss Agate ( Mockastein ) contains black Mangandendriten
  • Rainbow Agate ( shows as an interference effect of the thin layers of Newtonian color rings )
  • Tube agate ( Verdrängungsmorphose of long prismatic crystals )
  • Snakeskin Agate (aggregates with snake skin pattern )
  • Skolezitachat ( pseudomorphs after Skolezit )
  • Star agate geodes are usually irregularly shaped and completely filled when grinding often show a five-pointed shape.
  • Agate debris ( again cemented by tectonics broken and mineral deposition agates )
  • Turritella agate

Education

Agates form in rock cavities as the lining or filling: In (complete ) filling one speaks of an almond, at ( incomplete ) lining of a geode. As rock cavities are primarily hollow cavities in volcanic rocks into account, here is the contained in the flowing lava gases no longer pushed to the surface of the lava flow through and could not escape, but they were included in the growing cold lava, forming a cavity therein, the be completed in a later process with agate, quartz, calcite or other mineral substances. As volcanic rocks are both basic volcanic rocks, such as basalt, and acidic volcanic rocks, such as rhyolite, into consideration.

This bubble spaces in volcanic rocks are the most common places where agates may arise, however, agates are formed also in corridors and crevices of different rocks and also in cavities of sediments. Also in fossils, such as petrified trees, in silicified corals and dinosaur bones agates are observed.

With the question of how the silicon dioxide-containing material has penetrated into these cavities, numerous mineralogists have employed in the last 200 years, and established several theories. This had to be clarified, such as in a basalt, so in a basic, low- silicate rock could occur such accumulation of pure SiO2. Here is the originally present thesis that the SiO2 accumulation had taken place already in the molten rock and are said to have the red-hot molten magma already deposited drops of liquid silica, now regarded as obsolete, if only because agates are also found in rocks, that were never in glutflüssigem state ( see above). Today, the unanimous opinion is expressed that agates are called sedimentary - diagenetic range, ie at temperatures up to 200 ° C, emerged.

Furthermore, the hypothesis was considered that siliceous aqueous solutions are invaded by so-called infiltration channels in the rock cavities, have settled on the cavity wall and then leave the cavity again agate band. After several repetitions of this process, the cavity is gradually filled with agate. This so-called infiltration theory presupposes the dubious transporting large amounts of water in the rock and is therefore no longer recognized today.

In the search for a solution of the problem today agate is a theory in the foreground, which has been developed by Michael Landmesser at the Institute of Gemstone Research in Mainz. Surveyor assumes that the rock next to larger cavities a network of the finest hairline cracks and capillaries is present that is constantly filled with water and in which the required for the accumulation of silica is transported in the form of mono silicic acid H4SiO4 by diffusion. After Landmesser ie not the transport of large quantities of water, but the diffusion process of mono silicic acid plays a crucial role in the agate genesis. The mono silicic acid molecules react with each other in a continuous process of accumulation, in which the molecules via common oxygen atoms to Dikieselsäuren, Trikieselsäuren, tetra silicic unite and so on until eventually emerge colloidal polymeric silicic acids, which are reflected on the walls of the cavity due to adhesion and in a maturation process (especially discharge of water ) eventually turn into solid cryptocrystalline quartz. This process takes place over long periods, in which the external conditions such as pressure, temperature, presence of accessory minerals, such as Fe 3 compounds change, resulting in the formation of the characteristic Achatbänderung.

Locations

Europe

  • Germany Baden- Württemberg: Lierbachtal at Oppenau / Schwarzwald, Stretch Sandweier in Baden -Baden, Unteralpfen in Waldshut
  • Bavaria: Sailauf in Aschaffenburg
  • Brandenburg: Saalhausen ( Grossraeschen ) in Senftenberg
  • Rhineland -Palatinate: Region Idar -Oberstein Idar -Oberstein Steinkaulenberg, Idar -Oberstein Stbr. Setting, Vollmersbach in Idar -Oberstein, Fischbachtal Stbr. Juchem, Fischbachtal Stbr. Bernhard, Quarry Hellberg in Kirn, Rimsberg in Birkenfeld, Dienstweiler in Birkenfeld, Baumholder Stbr. Backes mountain, Baumholder military training area, Oberhausen an der Nahe, Reichweiler at Freisen etc.
  • Palatinate Forest: Albers hamlet near Annweiler, Waldhambach (Pfalz ) at Annweiler,
  • Rheinhessen: Imsbach at Thunder Mountain, Nack at Alzey, spiral near Alzey, Bad Sobernheim
  • Eifel: gravel pit Arenrath at Binsfeld

Africa

  • Algeria: Oasis Tidikelt / Sahara
  • Botswana: Bobonong, Mashuta
  • Malawi: Ngaba
  • Madagascar: Mahajanga Province
  • Morocco: Tizi -n- Tichka, Asni, Sidi Rahal in the High Atlas, Aouli, Kerrouchen, Zaër - Zaïane
  • Namibia: Agate Bay at Luderitz, Skeleton Coast, Grunau in southern
  • South Africa: Lichtenburg
  • Tanzania: Kigoma and Morogoro

North America

  • USA: Arizona: Mulligan peak at Clifton
  • California: Mojave Desert
  • Florida: Tampa Bay
  • Minnesota: Duluth on Lake Superior
  • Montana: Dryhead Ranch / Pryor Mountains, Yellowstone River
  • Nevada: Black Rock Desert
  • New Mexico: Baker Egg Mine near Deming
  • Oregon: Priday ( = Richardson ) Ranch / Ochoco Mountains, Morrison Ranch
  • South Dakota Black Hills in Fairburn, Tepee Canyon
  • Texas: Woodward Ranch in Alpine
  • Utah: Dugway geode beds at Vernon, Hanksville, Crescent Junction with Moab
  • Wyoming: Blue Forest

South America

  • Argentina: San Rafael / Mendoza Province with the Directory Canon de Atuel, Cerro Victoria, Sierra Pintada, inter alia, Malargüe / Mendoza Province, pajaritas / Chubut Province
  • Brazil: Rio Grande do Sul, Minas Gerais, Soledade in the State of Paraiba
  • Uruguay: Artigas

Asia

  • China: Nanjing
  • India: Deccan Plateau
  • Indonesia: Donorojo on the island of Java
  • Kazakhstan: Maiskoje at Semipalatinsk
  • Turkey: Çubuk in Ankara
  • Mongolia: Burugdi / Gobi desert

Australia and New Zealand

  • Agate Creek / Queensland, Mount Hay / Queensland, Wave Hill pastoral station / Northern Territory
  • Mount Somers / Ashburton District on the South Island

Further sources see

Morphology

The structure of agates usually consists of concentric or irregular layers, filling a cavity. The agate is composed of different varieties of chalcedony, microcrystalline silica. The individual layers show coarser and finer structures and are often extremely thin, so that a few hundred come to 1 mm. Full amorphous ( hydrous ) silica comes in the agates in any case very rare. The different color usually comes from iron and manganese compounds ago, but the onyx (black and white layers ) and Sardonyxe (red and white layers ) usually colored artificially. Place between and above the chalcedony usually drusige Amethystlagen. Very often encloses the almond a hollow space drusen, which still rock crystal, amethyst, calcite, zeolites, hematite and other minerals come to training. In Oberstein all Chalcedonlagen the outer almond shape to nestle, found in the Brasilian almonds in the interior usually a layer plane-parallel horizontal layers. Not infrequently, the channels are laid bare when looping through which, has entered the almond space the inner mass, or rather the liquid which it contained solved. This is therefore formed first, and from outside to inside the individual layers are deposited from aqueous solution progressively wherein the deposited mineral often the nachdringenden fluid clogged the road, and so was left inside a cavity.

After the disintegration of the matrix in which the agates were embedded, they are free and by their siliceous nature, which is extremely resistant to corrosion by air or water, remain as nodules in the soil and gravel obtained even when they rolled into rivers be.

Agate is quite resistant mineral and also shows no reaction to water or sunlight. Also from scratches and cracks, he is quite well protected, as it has high hardness and density.

Use

Agate and its varieties found mainly as a gemstone use. By coloring and drawing excellent agates since time immemorial to cut stones were ( gems, cameos, signet rings ), but also mortars and mortars, Glättsteinen, ring stones, clasps, bracelets, rosaries, stick buttons, knife handles, Schussern and many other decorative or useful objects processed.

Because of its high hardness and resistance to chemicals Agate is also used increasingly in the art.

Manipulation and imitation

Following the fashionable taste, use is made of the possibility in the jewelry industry in many ways to color the agate, which is based on the different nature of the individual layers of the stone, of which some are porous enough to absorb liquids, the other not.

For example, most Onyxe be artificially generated by the agate is warmed two to three weeks in dilute honey or sugar solution and then boiled in concentrated sulfuric acid. After it has dried, it is cut, added a day in oil and washed off at the end with bran. The porous layer in which the invading honey has been charred by sulfuric acid, the impenetrable white crystalline layer appears depending on the porosity of gray, brown or black, even brighter and shinier. Through various chemicals to any color can be produced, provided that the agate absorbs liquid spills.

Before the processing of the stone is often burned in order to change its color, and then laid still to two weeks in sulfuric or nitric acid. But the coloring is usually performed only on the polished stones, although the color penetrates deep into the mass of stone and stands out clearly on the break more or less.

Is Agate recolored in naturally occurring colors, this can only be distinguished under the microscope from a genuine agate. Dyes, which do not occur such as cobalt blue, magenta, purple or pink, however, are easy to spot in natural agate.

There are also " artificial agates ," so-called Achates, colorful color, the agate like glass.

The declaration colored agates is voluntary and not mandatory.

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