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
|
Colour |
White, Pink, Block , Green, Shaded, Striped |
|
Luster/Gloss |
Glassy |
|
Reflectivity |
80-95% |
|
Transparency |
Translucent |
|
Hardness |
2.8-3.5 |
|
Abrasive Index |
8-42 |
|
Solubility |
Soluble residue negligible |
|
Sp. gravity |
2.7 - 2.9 |
|
Absorption |
Negligible |
|
Strength |
Capacity to resist stress, depends upon rift, hardness, degree of cohesion & interlocking (56-190mpa) |
|
Transverse Strength |
4.2 - 28 mpa |
|
Compressive Strength |
50 - 90 mpa |
Chemical Composition of Marble
Indian marble has the following main chemical constituents in its composition.
Soluble residue - 0.89%, Fe2o3 - 0.28%, CaCo3 - 97.74%, MgCo3 - 1.22%, Phosphoric Acid - 0.04%.
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.
(cn-stonenet.com) 
