Ophicalcite are metamorphic rocks with strongly fluctuating mineral composition and changing texture features. Its main components form carbonate minerals and magnesium-containing silicates, preferably the serpentine. The Ophicalciten used industrially is serpentinhaltige marbles and carbonate- to Serpentinitbrekzien.
The term ophicalcite is composed of the Greek root word Ophites ( snakelike ) and the Latin word calx (lime), specifically here of the mineral calcite name together. In the same sense certain bands -wound fine structures within a homogeneous mineral inventory of rocks with the word ophiolitisch ( snake -like impression ) are characterized. The thematically closely related term " serpentine " or " serpentine " comes from Latin and refers to the same optical appearance ( Snake: Latin serpens ).
Formation and mineral composition
Because Serpentinitmineralien emerge from complex transformations of ultramafitischen parent rocks, also very different color and texture forming mineral components may be included in a ophicalcite. This results in the formation of Ophicalciten if made on carbonate rocks (limestone, dolomite, magnesite) Mg silicate Metasomatosen ( conversion by mineral replacement) by metamorphic processes of different intensity. Besides, numerous new minerals are formed, such as olivine, serpentine, magnesium chlorite, tremolite, talc and representatives of Humitgruppe. These minerals have a significant impact on color, texture and other optical or mechanical properties of the rock resulting from it.
Another and different type of formation process of Ophicalciten occurs when come together through processes of rock mechanics, ie by tectonically induced mixtures that already existing components separately (eg with large Ophiolitkomplexen the Südalpenzone ). A known form is the mixing of Serpentinitbrekzien with limestone by mechanical and hydrothermal ( by water and temperature caused solving ) processes. Rocks of this mode of origin can be found for example in Switzerland and northern Italy, where they are broken down as so-called green " marbles " (in the Aosta Valley).
Ophicalcite stand in the rock systematics between various other rock groups. These are serpentinites, peridotites, talc, chlorite and Amphibolgesteine . The mineralogical main feature is to be composed of approximately equal proportions of carbonate minerals (mainly calcite ) and serpentinite and olivine minerals (magnesium silicates). The rock term is also used in the case where a carbonate containing only minor amounts of Serpentinitmineralien.
The color features are very differentiated, because the group of silicates are many already from their initial state. In the serpentinization of peridotites occur chrysotile fibers ( Faserserpentin ). In addition, antigorite ( Blätterserpentin ) forms. The Serpentinarten and Peridot and chlorite are responsible for the green color. The decomposition of Olivinanteilen results in brown staining, because the iron ions of olivine transition to independent Fe - minerals. Talk deposits form a white to pale greenish color component. The calcite or other carbonates are usually white rock constituents. At petrophysical characteristics, the cracking and Klüftigkeit is emphasized by those Ophicalciten, which have formed by tectonic processes. The former mechanical stresses of a deposit are documented in the form of open cracks and hairline cracks. In the best case they are subsequently healed with calcite and solidify again in this way the deposit. Due to the retention of talc and chrysotile fibers mechanically unstable zones arise at higher local concentration (risk of breaking or chipping ). These areas take little or no polish. They can have the form of wires, tapes, or clouds. The described complex mineral composition leads to differentiated patterns and colors. In some quarries, these features vary from one another on a few meters away. The expected in the depth of such deposit varieties are difficult to predict, since exploration drilling indicate only a very limited visual impact for the expected material. If a quarry in a steep hillside created, there is the question of the reasonable expenses of such wells. In practice it is often so doing, that the rock produced is sorted according to optical characteristics, and sold under various trade names.
Occurrence, extraction and processing
In some European countries are Ophicalcite, mostly under the commercial group called " green marble " offered. Note that not all green marble-like rocks are automatically Ophicalcite. Important deposits are found in Italy (Aosta region ), Ireland Galway region ( Connemara ), Sweden Lake Vättern ( Brännlyckan ), in Turkey Afyon ( Usak ), Greece Euboea ( Styra ), in Portugal in Alentejo ( Alvito and Santiago do Escoural ), Spain in the province of Huelva ( Aroche ) and in Brazil in Minas Gerais ( Campos Altos ).
The extraction in the quarry is usually done by the Helikoidalsäge (a type wire saw ). In underground mining in addition a Schräme (sword or chain saw ) is still used. The ingots thus obtained usually have rectangular shapes and can now be sawn into individual slabs. The surfaces are polished, honed, sandblasted, bush-hammered or brushed or antiqued.
Foreign language names
English: ophicalcite, serpentine marble, French: ophicalcite, Spanish: oficalcite; Portuguese: oficalcite, Russian: офикальцит, Czech: ofikalcit, Polish: ofikalcyt.
Use and durability
The Ophicalcite be used similarly to the marble / limestone or Serpentinitgesteinen for decorative and architectural purposes for indoor and outdoor use. For construction of the road they are rarely used. In landscaping one uses it occasionally for heavy and light stone walls. In the northern Italian region of Aosta you can admire numerous and interesting façade designs in the form of perfectly crafted offset rubble masonry of chalets and houses. This is a mixture of serpentinite and ophicalcite - bricks. Chance also grave times and other monuments from Ophicalciten be made . The tapes, strip and power core structure of some varieties have a highly attractive. These varieties will find their use in the exclusive interior design. It is floor and wall coverings to furniture parts ( table tops, vanity tops, basins, kitchen slats ) and individual pieces for design purposes, and more artistic rules.
- Raymond Perrier: Les roches Ornementales. Ternay ( Edition Pro Roc ) 2004, ISBN 2-9508992-6-9
- Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks. Enke, Stuttgart 1985, ISBN 3-432-94671-6
- Metamorphic Rock