Stones
(g.k. goswami)
Marble is a rock widely used in buildings, monuments, and sculptures. It consists chiefly of calcite or dolomite, or a combination of these carbonate minerals. Marble is a type of metamorphic rock formed from limestone (see METAMORPHIC ROCK).
Most marble of commercial value was formed in the Palaeozoic Era or earlier in Precambrian Time. Marble is found in many countries, including Belgium, France, Great Britain, Greece, India, Italy, and Spain. South American nations also have large marble deposits. In the United States, Georgia produces the most marble.
Properties. Marble is formed from limestone by heat and pressure in the earth''s crust. These forces cause the limestone to change in texture and makeup. This 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 recrystallization affect the mineral composition of the marble that forms. 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 extremely high temperatures, rarer calcium minerals, such as larnite, monticellite, and rankinite, form 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 haematite and magnetite. In some cases, all these impurities may react to form garnets, hornblendes, and pyroxenes.Write your abstract here.
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