is a sedimentary rock, mainly composed of mineral calcite. The
primary source of the calcite is usually marine organisms, which
settle out of the water column and are deposited on the ocean
floors as pelagic ooze (but see lysocline for information on calcite
dissolution). Secondary calcite may also be deposited in super-saturated
meteoric waters, as is evidenced by the creation of stalagmites
of limestone emerge from the Earth's surface in often spectacular
rocky outcrops and islands. For example the Verdon Gorge in France,
Malham Cove in North Yorkshire, England and the Ha Long Bay National
Park in Vietnam.
consists of sedimentary rock wholly or in large part composed
of calcium carbonate. It is ordinarily white but may be coloured
by impurities, iron oxide making it brown, yellow, or red and
carbon making it blue, black, or gray. The texture varies from
coarse to fine. Most limestones are formed by the deposition and
consolidation of the skeletons of marine invertebrates; a few
originate in chemical precipitation from solution. Limestone deposits
are frequently of great thickness.
often tends to be more expensive than Marble, Travertine and Granite,
it also tends to be very popular with many discerning Architects,
Designers, Builders, and Consumers.
and More interior décor publications are emphasising on
the use of Limestone and Travertine not only as a wise investment
long-term to ceramics and terracotta but for the ease of maintenance
and overall appearance.
is quarried for roadbeds and gravel roads, building and landscape
construction, and cement manufacture.
SEDIMENTARY ROCKS GENERAL
Sedimentary rock is one of the three main rock groups (along with igneous and metamorphic rocks) and is formed in three main waysóby the deposition of the weathered remains of other rocks (known as clastic sedimentary rocks); by the deposition of the results of biogenic activity; and by precipitation from solution. Sedimentary rocks include common types such as chalk, limestone, sandstone, and shale.
rocks are formed from overburden pressure as particles of sediment
are deposited out of air, ice, or water flows carrying the particles
in suspension. As sediment deposition builds up, the overburden
(or lithostatic) pressure squeezes the sediment into layered solids
in a process known as lithification ("rock formation")
and the original connate fluids are expelled.
rocks are composed largely of silica (i.e. quartz), with other
common minerals including feldspars, amphiboles, clay minerals
and sometimes more exotic igneous minerals. Sedimentary rocks
are classified as clastic, that is, they are composed of discrete
clasts of material (rather than being composed of organic material
as is the case for a limestone).
minerals precipitating out of the ocean cover the ocean floor
with layers of calcite which can later form limestone.
rocks are economically important in that they can be used as construction
material. In addition, sedimentary rocks often form porous and
permeable reservoirs in sedimentary basins in which petroleum
and other hydrocarbons can be found.
is believed that the relatively low levels of carbon dioxide in
the Earth's atmosphere, in comparison to that of Venus, is due
to large amounts of carbon being trapped in limestone and dolomite
sedimentary layers. The flux of carbon from eroded sediments to
marine deposits is known as the carbon-cycle.
shape of the particles in sedimentary rocks has an important effect
on the ability of micro-organisms to colonize them. This interaction
is studied in the science of geomicrobiology. One measure of the
shape of these particles is the roundness factor, also known as
the Krumbein number after the geologist W. C. Krumbein.
rock is one of the three main rock groups. See also igneous and
rock is formed from the weathered remains of other rocks.
CLASSIFICATION OF ROCKS