Sunday, 5 April 2015

Marble

Marble
Marble is a metamorphic rock which is non foliated and is formed when limestone is subjected to heat and pressure where calcite recrystallizes to form a rock that is a mass of interlocking calcite crystals. In marble not all of the rock is formed of calcite other minerals can also be present such as clay minerals, micas, quartz, pyrite, iron oxides and graphite. Same as of the limestone marble, dolostone when metamorphose produces dolomitic marble.

How does marble forms?

Marble is a rock resulting from metamorphism of calcite bearing limestone or dolomite rock. The resulting marble rock is typically composed of an interlocking mosaic of carbonate crystals. Primary sedimentary textures and structures of the original carbonate rock have typically been modified or destroyed. As metamorphism progresses the crystals in the marble grows large enough to be recognized easily the interlocking of calcite.

Physical properties of marble and uses

Colour of marble

Pure white marble is the result of metamorphism of a very pure limestone or dolomite protolith that is silicate poor rock. The characteristic swirls and veins of many coloured marble varieties are usually due to various mineral impurities such as clay, silt, sand, iron oxides or chert which were originally present as grains or layers in the limestone. Green colouration is often due to serpentine resulting from originally high magnesium limestone or dolostone with silica impurities. These various impurities have been mobilized and recrystallized by the intense pressure and heat of the metamorphism.

Acid reaction

As marble is composed of calcium carbonate so it will readily react with acids to neutralize it. It is one of the most effective acid neutraliser. It is one of the most important acid neutraliser used in lakes. streams and soils. It is used for acid neutralization in the chemical industry. Pharmaceutical product known as "Tums" is a small calcium carbonate pill, sometimes made from powdered marble that is used by people who suffers from acid indigestion,

Hardness

Being composed of calcium carbonate marble has a hardness of three on the Mohs scale so marble is easy to carve for sculptures making and ornamental purposes. The low hardness and solubility of marble makes it suitable for calcium additive in animal feeds.

Polishes easily

After being sanded with progressively finer abrasives, marble can be polished to a high luster. This allows attractive pieces of marble to be cut, polished and used as floor tiles, architectural panels, facing stone, window sills, stair treads, columns and many other pieces of decorative stone. 

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