STONE HISTORY

ABOUT INDIAN STONES
Stones are classified based on their mineral content and the process of their formation. Good stones are characterized by durability, hardness, strength, compatibility to dressing, appearance, density, fineness of grain and compactness and porosity and property of absorption. For being suitable as building stone, a rock should have specific qualities such as capacity to stand the damage caused by time and weather, sufficient strength to take up strain and super-incumbent weight and attractive colours and general appearance for aesthetic acceptability. Its structure must also be such as to allow quarrying into sufficient sized blocks or sheets. It should possess inherent features such as joints and (in sedimentary rocks) bedding planes. India has extensive deposits of different kinds of building and monumental stones and is one of the few major countries known for the production and export of granites and marbles of various colours, along with slate and other building stones. The most important building stones in India are the granites/and allied rocks, the standstones, limestones and marbles, and the laterites.

IGNEOUS STONES
Igneous stone ranges from very soft rocks such as pumice and scoria to somewhat harder rocks such as tuff and hard rocks such as obsidian, granite and basalt. Igneous stones are formed from molten or partly molten material i.e. magma, through solidification of magma. Lava is a form of magma that 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 colours. From 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 colour 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 chemical structure, granite is a much harder stone. It doesn't get scratched as easily and rarely needs heavy-duty grinding.

SEDIMANTORY STONES
There are two main types of sedimentary stone used in masonry work, limestones and sandstones. 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. 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.

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".

GRANITE
The word granite derives its name from Latin "granum", meaning a grain, that represents the coarse-grained structure of this crystalline rock. Basically, granite is an igneous rock that is formed from magma. Granite is usually white or light brown in colour. They are also available in pink, gray or black colours based on their chemistry and mineralogy. Granite is usually a medium to coarsely grained rock. It is a hard and tough stone and is widely used as a construction stone.

PHYSICAL PROPERTIES OF GRANITE
Granite is composed mainly of quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. This mineral composition usually gives granite a red, pink, gray, or white color with dark mineral grains visible throughout the rock.
> Composition:Quartz and Feldspar with minor amounts of mica, amphiboles and other minerals.
> Hardness:Hard – difficult to scratched.
> Tendencies:High resistance of oils and liquids.
> Colors:Colors vary widely
> Porosity : Quite Low
> Density : 2.6 to 2.8 Kg/Cubic Meter

CHEMICAL PROPERTIES OF GRANITE
Granite is a hard igneous rock having a coarse-grained surface, chiefly composed of four minerals viz., quartz, alkali feldspar, plagioclase feldspar, and hornblende. These minerals provide the different colors to the granite that it possesses. Granite being an igneous rock, is formed from the process of magma cooling. This magma, which cools far below the earth's surface at a slow and steady rate, results in the expansion of the aforementioned minerals to a level that they can be conveniently seen with naked eyes. An important thing about granite is that it is not a homogeneous rock, thus its chemical properties vary according to its location. The worldwide standard of the average proportion of different chemical components that are present in granite is given below: