Marble
Marble, formed from limestone with heat and pressure over years in the earth's crust. These pressure or forces cause the limestone to change in texture and makeup. The process is called recrystallization. Fossilized materials in the limestone, along with its original carbonate minerals, recrystallize and form large, coarse grains of calcite.
Impurities present in the limestone during the recrystallization period affect the mineral composition of the marble which is formed. At relatively low temperatures, silica impurities in the carbonate minerals form masses of chert or crystals of quartz. At higher temperatures, the silica reacts with the carbonates to produce diopside and forsterite. At a very high temperatures, rarer calcium minerals, such as larnite, monticellite, and rankinite, forms in the marble. If water is present, serpentine, talc, and certain other hydrous minerals may be produced. The presence of iron, alumina, and silica may result in the formation of hematite and magnetite.
The minerals that result from impurities give marble a wide variety of colors. The purest calcite marble is white in colour. Marble containing hematite are reddish in color. Marble that has limonite is yellow, and marble with serpentine is green in colour.
Marble does not split easily into sheets of equal size and must be mined with care. The rock may shatter if explosives are used. Blocks of marble are mined with channeling machines, which cut grooves and holes in the rock. Miners outline a block of marble with rows of grooves and holes. They then drive wedges into the openings and separate the block from the surrounding rock. The blocks are cut with saws to the desired shape and size.
Physical Properties of Marble
Physically, these are recrystallized, Hard, Compact, fine to very fine grained metamorphosed rocks capable of taking shining polish. Hardness 3 to 4 on Moh's Scale
Density 2.55 to 2.7 Kg/cm3
Compressive Strength 70 to 140 N/mm2
Modulus of Rupture 12 to 18 N/mm2
Water Absorption Less than 0.5%
(except Rainforest Green/Brown with 2-3%)
Porosity Quite low
Weather Impact Resistant
Chemical Properties of Marble
Chemically, they are crystalline rocks composed predominantly of calcite, dolomite or serpentine minerals. The other minor constituents vary from origin to origin.Lime (CaO) 28-32%
Silica (SiO2) 3-30% (varies with variety)
MgO 20 to 25%
FeO + Fe2O3 1-3%
Loss On Ignition (LOI) 20-45%
Uses of Marble
Marble has always been highly valued for its beauty, strength, and resistance to fire and erosion. The ancient Iranian & Greeks were good user of marble in their buildings and statues. The Italian artist Michelangelo used marble from Carrara, Italy, in a number of sculptures. Marble from Tennessee was used in parts of the National Gallery of Art in Washington, D.C. The Lincoln Memorial, also in Washington, was built of marble from Alabama, Colorado, and Georgia.
Very pure calcite marble is used for most statues. They are translucent. Large blocks of colored marble are used for columns, floors, and other parts of buildings. Smaller pieces of marble are crushed or finely ground and used as abrasives in soaps and other such products. Crushed or ground marble is also used in paving roads and in manufacturing roofing materials and soil treatment products.
Textures of Marbles
Marbles show variety of textures on account of existing minerals & re-crystallization patterns. Texture depends upon form, size, uniformity of grain arrangements. Marbles can be classified on the basis of the following factors :-
Calcite Marble - Mostly CaCo3; MgCo3<0.50%
Dolomite Marble - Having > 40% MgCo3
Magnesium Marble - MgCo3 between 5 to 40%
Serpentine Marble - remobilised marble due to the effect of Thermodynamic metamorphic wherein serpentine is prominent
Onyx Marble - Lime carbonate deposition on account of cold water solution activity
Impurities in Marble
The following are the major mineral impurities in marble:
Quartz
Tremolite Actinolite
Chert
Garnet
Biotite
Muscovite
Microline
Talc
Fosterite
The following are the major chemical impurities in marble:
SiO2
Fe2O3
2Fe2O3
3H2O
Limonite
Manganese
Al2O3
FeS2(pyrite)
On account of the mineral composition of marble the colour variations
Ocurrances of Marble
Spain :Andalucia region: El Monte Coto
Italy: Carrara
India: Masaron Ki Obri, Rishabhdeo (Kesariyaji), Udaipur, Rajasthan
Nai Parbati, Amet, Dist. Rajsamand, Rajasthan
Manpura, Dhariyawad, Dist. Udaipur
Sidhavatam, Kadapa Dist., Andhra Pradesh
Umpavally, Koraput Dist., Orissa
Australia: Buchan in Victoria, Bathurst/Orange in N.S.W., Ulan in Queensland
Namibia: Palisandro marble quarry 45 km south-east of Karibib
China :Southeast of Wumiao |