Onyx marble
The term onyx marble (sometimes shortened to "onyx") is applied to certain limestones ( sedimentary rock ) and is derived from their appearance. From a petrographic point of view, it is doubly misleading as it is neither marble nor onyx ; However, this term has become firmly established among processors and art.
The term “alabaster marble”, often shortened to “ alabaster ”, is also not applicable from a petrographic point of view, and it has become solidified in archeology, for example.
Explanation of terms
This rock group is limestone sinter (freshwater limestone ), which was formed by the precipitation of the finest limestone particles from spring water, underground freshwater courses (in karst areas) or from seepage water in limestone deposits with natural cavities. Sometimes cryptocrystalline (appearing amorphous) or extremely crystalline sintered limes arise. In geology, rocks of this type are also referred to as quaternary limestone (geological quaternary ) or spring limestone . A few occurrences arose before the Quaternary.
Onyx marbles consist of the minerals calcite or aragonite . Both are modifications of the chemical compound calcium carbonate . It is non-marine (therefore freshwater limestone), chemical sediments .
In principle, the stalactites ( stalactites , stalagmites ), if they are made of lime, also belong to it. In the past, these natural beauties were obtained on a small scale from certain caves and processed for decoration or jewelry purposes. Because these columnar deposits only allow small raw pieces to be mined, the supplies are relatively small and awareness of nature conservation spread in this sector as early as the 19th century, modern applications were only possible to a very limited extent. The mostly ring-shaped structure in cross-section severely restricts the possible uses. Today it goes without saying that caves are no longer plundered because of this "raw material".
Most onyx marbles have the property that they are very transparent in the light and can therefore achieve an interesting effect. For this reason they were z. B. used as a church window in Orvieto Cathedral . Periodically deposited mineral impurities often result in very attractive bands in cross-section (gdL - against the bearing). In most cases, these are deposits of compounds of divalent and trivalent iron.
Onyx in the geological sense is a variety of quartz that is not involved in the formation of onyx marble.
Marble in the geological sense is a metamorphic limestone. But because marble has been used as a cultural word for all polishable limestones since ancient times and a banding similar to real onyx often occurs, the term onyx marble has become established among processors, dealers and in art.
The term "alabaster marble" is also wrong from a petrographic point of view, but it refers to the comparable visual appearance of real alabaster . The use of this term can be traced back about two hundred years in the literature. Alabaster is correctly understood as a rock that consists of the mineral gypsum (calcium sulphate).
Other common terms are lime onyx, calcite- alabaster, ribbon marble, aragonite marble or marble onyx.
These examples show how stone names in the area of natural stone applications are strongly dependent on cultural and aesthetic influences. Such terms are not only limited to the natural stone trade, but can also be found in many serious cultural-historical and art-scientific contexts.
Foreign language terms
English: onyx marble, fresh water limestone, cave onyx ; French: onyx calcaire ; Italian: onice, stalattite, alabastro fiorito, alabastro ; spanish: alabastro calizo ; Portuguese: estalactite, concreção calcária, onix ; Russian: натечный кальцит; Czech: onix, vapenný sintr ; polish: onyx, kalcyt naciekowy, inkrustacja węglanem wapnia ; Hungarian: mészlerakódás ; Romanian: Concreţiune calcaroasă ; Slovak: ónyxový mramor , ónyx .
Modifications
The cryptocrystalline types of onyx marbles are those with the greatest transparency. Numerous varieties show clear transparency in the light even with a material thickness of three centimeters.
The variety of ligaments is very large in numerous varieties. Common colors are white, yellow, orange, red and green, in all conceivable shades. Those deposits are considered to be particularly attractive if they produce a multicolored picture due to changing mineral deposits.
When cutting with the camp (mdL) - i.e. in the level of the sedimentation - sometimes bizarre, bulbous or coral-like structures result, which are particularly attractive when there is a differentiated play of colors.
The recognizable crystalline onyx marbles show when cut against the bed (gdL) - i.e. perpendicular to the level of the sedimentation - mostly long, slender and pointed crystals. These represent a modification of lime, called aragonite in mineralogy . Any existing bands run at an angle of about 90 degrees to the longitudinal axis of the aragonite crystals and thus characterize the sedimentation plane. The most common colors are between light yellow, brownish and reddish tones.
Deposits
Deposits of onyx marbles ( calcareous sinter ) can be found in numerous regions around the world. They are mostly associated with travertine deposits because travertines are created in a similar way. Nevertheless, they represent an independent rock group.
The stratigraphic classification is by no means uniform. Onyx marbles are generally referred to as Quaternary formations. This also applies to some occurrences.
A typical type of deposit are nest-like or cavernous (local cavities) deposits in limestone or travertine deposits. They enable only small quantities to be extracted. Often, thin banks with a thickness of a few decimeters can also be observed. Here only flat raw blocks can be obtained for processing.
Only a few deposits in the world have large bank thicknesses, which enable the mining of large blocks and thus the production of large sawn raw panels. In many deposits there is a mixture of lime sinter and normal lime / travertine. This reduces the visual attractiveness of the onyx marble or causes natural mechanical instability. Cracks and easily breaking workpieces are the result. For this reason, a lot of material has to be sorted out during mining - which gives the end products their high sales price - or the raw products are strengthened with a special synthetic resin.
In the history of application of onyx marble, in addition to some larger deposits, numerous small deposits have also been used that are no longer available today due to mining. Some information on deposits with a certain significance can be found below:
Africa
- Egypt, Wadi Sannur near Beni-Souef
- Egypt, Bosra Wadi near Assiut
- Algeria, near Nédroma and Hadjadja in the province of Tlemcen
- Algeria, near Bou-Hanifia in the province of Oran
America
- Mexico, no details
- Argentina, in the province of San Luis
- Brazil, no details
Asia
- Iran, at Dehkharegan near Maragha on Lake Urmia
- Pakistan, in the Chagai Mountains in the Baluchistan Province
- Turkey, Harmandali near Akhisar in the Manisa province
Europe
- Germany, Böttingen on the Swabian Alb
- France, at Amélie-les-Bains-Palalda in the Dep. Pyrénées-Orientales
- Italy, near Albino in Val Seriana in the Bergamo region
- Italy, near Duino in the Trieste Karst
- Italy, near Laas in South Tyrol
- Slovak Republic, near Levice
- Slovenia, near Gorjansko in the Slovenian Karst
- Czech Republic, in the Karlovy Vary headwaters, northern Bohemia
- Austria, Styria in Maria Buch
gallery
Böttinger ribbon marble from Böttingen / BW (D).
Onyx marble Akhisar Onyx Honey from the region Akhisar (TR).
Onyx marble Akhisar Onyx Red / White from the region Akhisar (TR).
Onyx marble Buthag from Pakistan (approx. 22 × 15 cm).
Onyx marble from the Tlemcen region (DZ).
Yazd onyx marble from the Yazd region (IR).
literature
- George P. Merrill: The onyx marbles: Their origin, composition and uses, both ancient and modern. Smithsonian Institution, United States National Museum, Washington 1895.
- Rosemarie Klemm, Dietrich D. Klemm: Stones and quarries in ancient Egypt. Berlin / Heidelberg 1993, ISBN 3-540-54685-5 .
- Gabriele Borghini: Marmi antichi. Roma 2001, ISBN 88-8016-181-4 .
