About 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.

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.

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