Building Stones
India
possesses extensive deposits of different kinds of building
and monumental stones. It is one of the few major countries
known for the production and export of natural building stones
of various colours. The most important building stones in
India are the granites/and allied rocks, sandstone, limestone
and marble. The different types of stones are:
Igneous Stones
Igneous
stones are formed from molten or partly molten material i.e.
magma, through solidification of magna. Lava is a form of
magma cools and solidifies on the surface of the earth. Liquid
magma cools and solidifies underneath the Earth's surface,
and then mineral gases and liquids penetrate the stone and
create new crystalline formations and various colors.
Of all igneous rocks, granite is the most common choice. It
is a coarsely crystalline unstratified igneous rock composed
of alkali feldspars, quartz, mica and hornblende. Since granite
is highly speckled, it varies greatly in color depending on
the range of the minerals present and the location of the
quarry. When the mica in granite is white, it is known as
muscovite, when it is dark it is biolite. In certain types
of granite, hornblende is an important ingredient and it may
be even more abundant than the micas. Due to its chemistry,
granite is a much harder stone. It doesn't scratch as easily
and rarely needs heavy-duty grinding.
Sedimentary stones
Sedimentary stones are layered rocks,
formed through the accumulation and solidification of sediments,
which may originally be made up of minerals, rock debris,
or animal or vegetable matter. These stones come from such
organic elements as glaciers, rivers, wind, oceans and plants.
Tiny sedimentary pieces break off from these elements and
accumulate to form rock beds. They are bonded through millions
of years of heat and pressure and include limestone, sandstone
and travertine. The different types of sedimentary stones
are:
- Some stone types are the result
of some pre-existing rock's demise through the weathering
process. Sandstone "Siliceous".
- The biogenic stones are produced
by living organisms such as marine creatures or vegetation
which eventually died and the remains became part of the
sediment on the bottom of ancient sea beds. Certain Limestone's,
Coralstones, Fossilstone, Shellstone "Calcareous".
- The third is produced by inorganic
chemical material being deposited on the floor of ancient
sea, lake beds and springs through the process of precipitation
or evaporation. The white fur deposits in kettles in which
hard water has been boiled is a good example of this type
of stone. Certain Limestone's and all Travertine's "Calcareous".
- The last sedimentary category are
produced as a result of volcanic activity. This stone is
composed of volcanic ash with a variety of secondary older
rock materials from the surrounding area, volcanic and igneous
in nature. This category is considered a tuff sedimentary
stone. It is also classified as a igneous stone due to its
volcanic origin. Cantera and Adoquin are of this variety
"Siliceous".
Metamorphic stones
Metamorphic
stones are formed in some fashion from a pre-existing rock,
through heat, pressure, the effect of superheated fluids,
or any combination of these forces. The change can be a development
of crystalline formation, a texture change or even a color
change.
Metamorphic is derived from the Greek word "meta" denoting
a change and "morph" meaning form or a change in form. This
changing of one rock type into another new type takes place
by an increase in temperature or pressure or a combination
of both. The original minerals of the stone recrystallize,
small crystals merge to form larger crystals with no changes
in the mineral chemistry, fine-grained calcite in limestone
recrystallizes to a coarse-grained calcite crystal structure
in marble; or there may by a transformation into a different
set of metamorphic minerals. This recrystallization transforms
the Shale into a colorful Slate "Siliceous". Limestone becomes
a multi colored Marble "Calcareous" and the grainy Sandstone
alters into a highly crystallized sparkling Quartzite "Siliceous".
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