Limestone
Limestone is a
sedimentary rock composed largely of the
mineral calcite (calcium carbonate: CaCO
3). Limestones often contain variable amounts of silica in the form of
chert or
flint, as well as varying amounts of
clay,
silt and
sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly
marine organisms. These organisms secrete shells that settle out of the water column and are deposited on
ocean floors as
pelagic ooze or alternatively is conglomerated in a coral reef (see
lysocline for information on calcite dissolution). Secondary calcite may also be deposited by
supersaturated meteoric waters (
groundwater that
precipitates the material in
caves). This produces
speleothems such as
stalagmites and
stalactites. Another form taken by calcite is that of
oolites (oolitic limestone) which can be recognised by its granular appearance. Limestone makes up about 10 percent of the total volume of all sedimentary rocks.
Pure limestones are white or almost white. Because of impurities, such as
clay, sand, organic remains,
iron oxide and other materials, many limestones exhibit different colors, especially on
weathered surfaces. Limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite,
quartz,
dolomite or
barite may line small cavities in the rock.
Folk and
Dunham classifications are used to describe limestones more precisely.
Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls and around
hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution that is supersaturated with chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls.
Coquina is a poorly consolidated limestone composed of pieces of
coral or
shells.
During regional
metamorphism that occurs during the mountain building process (
orogeny) limestone recrystallizes into
marble.
Limestone is a
parent material of
Mollisol soil group.
Image:LimestoneWithFossilUSGOV.jpg|Limestone with bivalve fossilsImage:Fossils-CastleHain.jpg|Various fossils collected from a limestone quarry, North Carolina USA. Clockwise from upper left: echinoids, bryozoans, and brachiopodsImage:Limestone saw Belgium.jpg|Water cooled limestone saw, Belgium*
List of minerals*
List of rocks*
Aragonite*
Blisworth Limestone*
Calcite*
Calcium Carbonate*
Chalk*
Coral sand*
Dolomite*
Indiana limestone*
Ketton Stone*
Marble*
Oamaru stone*
Portland Limestone*
Quicklime*
Solnhofen limestone*
Quarry
