Marble
Marble is a nonfoliated metamorphic rock resulting
from the metamorphism of limestone, composed mostly of calcite (a
crystalline form of calcium carbonate, CaCO3). It is extensively used
for sculpture, as a building material, and in many other applications.
The
word "marble" is colloquially used to refer to many other stones that
are capable of taking a high polish.
A metamorphic
rock resulting from regional or rarely contact metamorphism of
sedimentary carbonate rocks, either limestone or dolomite rock, or
metamorphism of older marble. This metamorphic process causes a complete
recrystallization of the original rock into an interlocking mosaic of
calcite, aragonite and/or dolomite crystals. The temperatures and
pressures necessary to form marble usually destroy any fossils and
sedimentary textures present in the original rock.
Pure white marble is the result of metamorphism of very pure
limestones. The characteristic swirls and veins of many colored 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 coloration 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.
From Wikipedia