Chalcedony

• Chalcedony

The Chalcedon ( Latinized form of the Greek χαλκηδών ) or in registered German spelling Chalcedony is a fibrous, microcrystalline Gefügevarietät of the mineral quartz.

According to ancient sources, the term chalcedony is valid for all fibrous forms of microcrystalline quartz (including quartzine ) weak for all but not colored, massive deposits of microcrystalline SiO2 or is used as a generic term for all forms of microcrystalline quartz ( flint, chert, agate, onyx, jasper ... ). These are, strictly speaking, but rocks, which consist of various Gefügevarietäten of the quartz, the SiO2 modifications Moganite and other coloring impurities. In modern mineralogy, the term chalcedony is narrower (see structure).

Chalcedony is colorless to bluish gray. Impurities cause a variety of colorations, usually brown, reddish or green. Chalcedony is translucent, opaque, has a waxy luster and has a Mohs hardness of 6.5 to 7 nearly as hard as quartz.

For other colors to use different names. Red to brown chalcedony is known as carnelian ( carnelian ), the green variety, which are colored by nickel oxide, called Chrysoprase ( artificially colored are called grüngebeizter agate) or plasma, emerald green chalcedony iron oxide obtained by their dark green color. Plasma is sometimes with small Jasper points found are similar to the drops of blood, which is why he is called Heliotrope ( Blutjaspis ) or misleadingly Bloodstone. The widely known as Bloodstone mineral is hematite, an iron oxide.

Other names that are found for chalcedony, are Jasponix, Massik, quartzine, Zoesit, blue moonstone or Californian and milk stone.

Etymology and history

The name first appears in Pliny the Elder in his Latin Historia Naturalis ( 77 AD. ) On. He appoints a stone called " Calchedon " under a listing of translucent jasper species. The name derives from the town of Chalcedon in Bithynia, one could make a relationship between the two designated without. The also by Pliny the Elder few sections previously described reddish- sparkling, but slightly blackish stone " Carchedon " ( dt: the Carthaginians; maybe it is garnet) has also been identified in the Middle Ages with the chalcedony. This was due to the well by 95 AD. emerging Greek word χαλκηδών ( school Greek pronunciation Chalcedon ), a hapax legomenon that is handed down in only one ancient source, namely the Book of Revelation. Here (Rev 21,19 EU) says of the heavenly Jerusalem:

However, it can not be determined which mineral was exactly meant in Revelation. The Vulgate put a word in some manuscripts not with " chalcedonius " but with " carcedonius " again; the two statements of Pliny were so confused in the Middle Ages. In the tradition of this time can be found under the name " chalcedony " according to Pliny's " Carchedon " the description of a reddish Karfunkels who has no similarities with today's mineral. Soon occurs in the description of the red back; the " Blackness" is for " pallor ", which was always emphasized. The description indistinctly become then leads to a redefinition that is literary palpable at Albertus Magnus: It provides the first description of Chalcedon, which no longer on Pliny, but rather fits the today containing the term mineral " A pale, dark-colored, somewhat duller stone " with an " almost transparent, muddy and dirty substance, such as lead, the silver mimics ". Until modern times, the word to the collective name for microcrystalline, feinstfaserige Crystals is.

Varieties

• Agate
• Chrysoprase
• Heliotrope ( Blutjaspis )
• Wood Stone
• Carnelian ( carnelian )
• Onyx
• Plasma is a leek green variety similar to the Prasem

Education and Locations

Chalcedony is formed together with quartzine and Moganite near the surface in both columns and cavities of acidic and basic igneous rocks ( red agate ), in columns of metamorphic rocks and in sediments (Flint, chert, petrified wood). In the formation of agates, one starts from a crystallization from a gel SiO2 or SiO2 - supersaturated solutions at temperatures between 25 and 200 ° C. In sedimentary formation chalcedony and quartzine crystallize either of SiO2 - containing solutions (eg petrified wood ) or be formed during diagenesis from opal skeletons of diatoms, radiolarians ( radiolarite ) or siliceous sponges ( chert ).

Furthermore Chalcedony is one of the cement phases in the pore spaces of sandstones.

• Blue in Namibia, Turkey and India
• Pink in Turkey;
• Red in Russia and India
• Dark green in Brazil and Ząbkowice Śląskie
• Sicily
• Saxony
• Bohemia
• Tirol

Microstructure

Modest, granular microstructure is characterized by the lack of a preferred orientation of the Chalcedonfasern. The individual Chalcedonfasern are rarely longer than 1-3 microns. Such granular chalcedony makes up the bulk of flint nodules.

From nodular structure is when the Chalcedonfasern starting radialstrahlig grow from a seed crystal and form spherical aggregates. The diameter of spherulites is usually from 0.1 to 0.2 mm. Globular graphite chalcedony forms the horizontally layered areas in agate geodes and occurs occasionally in Flint and chert. Under the polarizing microscope with crossed polarizers spherulites show a characteristic extinction image Bertrand'sche cross.

A parabolic structure forms when the Chalcedonfasern radialstrahlig grow on the surface of a rock cavity. Adjacent tufts interfering with each other in their growth. Even at small distance from the growth seed grow as only approximately parallel aligned fiber bundle in the cavity. Parabolic grown chalcedony forms the concentric bandings in agates. Under the polarizing microscope shows in the parabolic grown Chalcedonbändern the characteristic Runzelbänderung. It is characteristic of Chalcedony and is absent in quartzine.

Structure

The term is used for all chalcedony perpendicular to the crystallographic c- axis along the prism surfaces (110) or (110) grown fibrous depth crystals ( Flörke et al 1991). The fibers have a thickness of less than one micron and are typically twisted in the longitudinal direction. The optical character of the fiber direction is "length - fast". This means that the axle with the higher index of refraction in the crystal is oriented perpendicular to the fiber direction. This differs from another chalcedony fibrous microstructure variety of low- quartz, the quartzine. Quartzine is "length -slow ", that is, the higher refractive index of the crystal is parallel to the fiber direction.

Structurally, chalcedony is not very different from the low- quartz. Electron microscopic studies revealed but for all microcrystalline quartz varieties a very large density of lattice defects. It is characterized by a thick sequence of Verzwillingungen according to the Brazilian law. This can be thought of as a stack of (101) layers of right and left quartz. In microcrystalline quartz, these layers have variable thicknesses of a few unit cells. Structurally take Chalcedon and also quartzine thus an intermediate position between unverzwillingtem low quartz ( left or right hand quartz) and Moganite. This was not until 1994, approved by the IMA as your own SiO2 modification phase can be thought of as a low- quartz with the maximum possible number of Brazilian twins. Principles of right and left quartz the smallest possible thickness of only one unit cell form a regular sequence in Moganite. This close structural relationship is the reason that Chalcedon always also contains significant amounts of Moganite. Another characteristic structural feature of Chalcedon, the missing quartzine, is the twisting of the fibers around their longitudinal direction. This twisting takes place within a continuous crystal, and due to spiral crystal growth along the imperfections ( threading dislocations ).

Use

Chalcedony is one of the semi-precious stones and is used as a material for cameos, ring stones, seal stones, and many other decorative and utilitarian objects. It is processed for a long time and is therefore also frequently found in antiques. Large pieces are also provided material for columns, architectural ornaments, table tops and vases that are aufpolierbar through a beautiful polish. In Stone Age cultures chalcedony was used for the production of blades ( flint).

Precautions

In strong UV light, a color loss will affect the beauty of the stone, as well as in direct sunlight or excessive light exposure.