Marble it is a metamorphic rock, composed mostly of calcite and obtained by limestone metamorphosis. From a petrographic point of view, the marbles are limestone or dolomite with well-developed calcite crystals due to the metamorphic processes to which they were subjected. The most common colors for marble are white, gray, Gray, black and red, generally due to the impurities contained (red from Iron salts, brown from those of Manganese, graphite gray etc), and the venulation is due to the numerous cracks later filled with secondary calcite.
Marble is formed from limestone under the action of heat and pressure over the years in the earth's crust. These pressures or pressure forces cause the limestone to change its texture and appearance, process called recrystallization. Fossilized limestone materials, along with minerals, recrystallizes and forms large grains, coarse calcite.
Impurities present in the limestone during the recrystallization period affect / modify the mineral composition of the marble. At relatively low temperatures, silicon impurities form quartz crystals. At higher temperatures, silicon dioxide reacts with carbonates to produce diopsides or forsterites. At very high temperatures, rare calcium minerals turn to marble. Other minerals may form in the presence of water. The presence of iron, Aluminum and silicon can lead to the formation of hematite and magnetite.
Minerals from impurities give marble a wide variety of colors. The purest marble in terms of calcite is white. Marble containing hematite is reddish in color, the one containing limonite is yellow and the one containing serpentines is green.
Marble cannot be easily divided into sheets of equal size and must be handled with care. Marble blocks are exploited by machines that cut ditches and make holes in the rock. The delimitation of a marble block by the miners is done by drawing ditches and holes. The block is detached with wedges and special machines, the blocks thus obtained are cut with saws to the desired shape and size, after which it is finished and polished according to the requests.
The general physical properties of marble are hardness, density, compression etc. Most marbles (with very few exceptions) have the following characteristics:
- Hardness: 3 – 4 on the Mohs scale
- Density: 2.55 – 2.7 Kg/cm³
- Compression strength: 70 – 140 N/mm²
- How to break: 12 – 18 N/mm²
- Water absorption: less than 0,5%
- Porosity: low
In terms of chemical properties, marbles are crystalline rocks composed mainly of calcite, dolomite or serpentine minerals, together with other minor components that vary from origin to origin. One of the most important is mentioned:
- Where (High): 28-32%
- Quartz (SiO2): 30 – 30%
- Peridotit (MgO): 20 – 25%
- Bauxite (FeO and Fe2O3): 1-3%
- Lose calcination (LAW): 20-45%
Among the mineral impurities detected in marble we mention tremolite, actinolitul. gun, garnet, biotitul, talcum, fosterite etc.
The largest marble quarry in Romania is located in the Poiana Ruscai Mountains, Caraş-Severin county. The Rușchița quarry came into operation in 1884. The marble extracted here is white with shades of pink, bluish and gray, compact (98,11%), with small to medium saccharide structure, its special quality being appreciated abroad as well, being exported to France, Italy, YOUR, Germany, Austria, Hungary, Egypt etc. For the construction of the People's House – the current Palace of Parliament were used among other materials, 1.000.000 m³ of marble.
Agricin offers a wide range of materials from Italy, Greece, Spain, Turkey, India, Egypt, Iran or Lebanon, they have different sizes, thicknesses and finishes.
Description of terms used:
- metamorphic rocks – they arise from other rocks through the process of metamorphosis (transformation) product of pressures, high temperatures that lead to an exchange of chemical elements
- calcit – carbonate mineral very common in nature
- limestone – also called calcium carbonate, it is a sedimentary rock, dominant organogena, white, gray or yellow. The rock is composed mainly of the minerals calcite and aragonite, both of which have a chemical formula (CaCO3).
- dolomite – variety of limestone
- hematite – natural iron oxide, very rough, red or brown, with semi-metallic luster
- magnetite – black or dark gray iron ore found in eruptive rocks and has the property of attracting iron
- lime – crystallized or amorphous iron ore, yellow-brown or reddish to black, consisting of hydrated iron oxide, clay and a little phosphorus
- serpentine – mineral with varieties of different colors, resulting from the hydrolysis of magnesium silicate
- peridotit – peridotites are part of large-grained rocks, formed in the layers of the earth's crust, located at a depth of 200 – 300 km, containing at least 40 % olivină, the rest being composed of orthopyroxenes and clinopyroxenes, minerals with a high concentration of aluminum, magnesium, iron which depending on the temperature and pressure at formation are associated with garnet, spinel, rarely plagioclase
- bauxite – bauxite is one of the most important aluminum ores and is composed of most aluminum-containing minerals that: Gibbsit (Hydrargillit) Al (OH)3, Boehmit AlO (OH) and Diaspor AlO (OH). Bauxite may also contain iron minerals such as Hematite Fe2O3 and Goethite FeO (OH), as kaolinite clay minerals and minerals with a low titanium oxide content Anatas TiO2.
- quartz – or natural silicon dioxide, which is found in rocks in an unconsolidated state (like sand) or in the form of hexagonal crystals, transparent and colorless (in its pure state) or differently colored (when they also contain foreign substances)
- tremolit – natural calcium and magnesium silicate in the form of white crystals
- actinolit – shiny green stone with elongated radial crystals
- flint – natural variety of opal
- grenade – natural calcium silicate, of magnesium, iron, of manganese, aluminum or chrome, used as a grinding stone or, in its pure state (red), as a semi-precious stone
- biotit – small variety, green, brown or black
- significance – natural hydrated magnesium silicate, white-green color, greasy and soft to the touch
- fosterite – group of resins