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Sandstone
Sandstone, coarse-grained, sedimentary rock consisting of consolidated
masses of sand deposited by moving water or by wind. The chemical
constitution of sandstone is the same as that of sand; the rock
is thus composed essentially of quartz. The cementing material
that binds together the grains of sand is usually composed of silica,
calcium carbonate, or iron oxide. The colour of the rock is often
determined largely by the cementing material, iron oxides causing
a red or reddish-brown sandstone, and the other materials producing
white, yellowish, or greyish sandstone. When sandstone breaks,
the cement is fractured and the individual grains remain whole,
thus giving the surfaces a granular appearance. Sandstones of various
geological ages and of commercial importance are widely distributed.
Besides serving as a natural reservoir for deposits of oil and
gas, it is used in building and in the manufacture of whetstones
and grindstones.
In India a wide range of sandstones in different colour are available
these are generally found in the North of India , we give here some
of the sandstones that can be offered from India
Limestone
Limestone, a sedimentary rock consisting largely of calcium
carbonate (CaCO3), usually in the form of the mineral calcite.
It may be
produced biologically, chemically, or physically. Most of the
world’s ocean floors contain limestone that formed from
the shells of dead marine organisms (such as foraminifera)
that drifted downwards through the water and settled on the
sea floor.
A particular form of biological limestone, generated mainly
in shallow waters, is chalk, but not all limestone is chalk.
Coquina
and oolite are also organic forms of limestone. However, limestone
may also be produced chemically, being forced to precipitate
out from saturated seawater that can dissolve no more carbonate.
In rarer instances it may also be produced physically, by the
deposition of pre-existing limestone particles that have been
washed down by rivers, although rivers would probably dissolve
much of the limestone that entered them.
Limestone may contain a small percentage of the calcium-magnesium
carbonate mineral dolomite, CaMg(CO3)2, and still be called a
limestone, or sometimes dolomitic limestone. Moreover, unlike
chalk, a particularly
pure form of limestone, “limestone” may contain significant
amounts of non-carbonate material such as silica, feldspar, clay,
or pyrite.
When heated to a high temperature in a furnace, limestone is converted
to lime (calcium oxide, CaO), one of the chief uses of which is
as a fertilizer. However, limestone is also useful in its own right,
for example, as Portland stone, in building. Metamorphosed limestone
is known as marble, and is used for building and as an ornamental
stone. However, not all the so-called marble used by builders is
of true limestone origin.
From India we can offer quite a few varities of Lime stone which
are shown here . Slate
Slate, dense, fine-grained, fissile rock, formed by the metamorphism
of shale or clay, or more rarely of igneous rocks.
The process of metamorphism results in consolidation of the
original rock and in formation of new cleavage planes along
which slate
characteristically splits into thin, broad sheets. Many rocks
that show “slaty cleavage” are by extension loosely
called slate. True slate is hard and compact and does not undergo
appreciable
weathering.
The basic minerals comprising slate are quartz and muscovite,
a kind of mica; biotite, chlorite, and haematite are often present
as accessory minerals, and apatite, graphite, kaolin, magnetite,
tourmaline, and zircon may occur as minor accessory minerals.
Slate
is commonly bluish-black or grey-black in colour, but red, green,
purple, and variegated varieties are known; it is quarried in
Wales, France, Germany, and the United States. Slate is quarried
usually
in open pits and rarely in underground workings. The stone splits
best when it is “green”, or freshly taken from the
quarry. Slate is employed as a roofing material and for paving
stones, flooring, and traditional blackboards.
In India quite a large variety of slates are found particularly
in the south of our country , we give here some of the varieties
that can be offered from India
Quartzite
Quartzite, common and widely distributed rock composed mainly or
entirely of quartz. The compact, granular rock is a form of metamorphosed
sandstone in which silica, or quartz, has been deposited between
the grains of quartz of which the sandstone is essentially composed.
Other minerals that may be present in small amounts in quartzite
include feldspar, mica, rutile, tourmaline, and zircon. Quartzite
has a smooth fracture and is found primarily among ancient rocks.
In India quite a range of quartzite are available for various applications
and we give herewith some of the range that can be offered from
India
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