What is a Limestone?

Limestone is basically a stone that has been formed at the bottom of ocean or lake from shells, bones or remaining hard objects of fish or corals. They are of sedimentary origin and composed principally of calcium carbonate or the double carbonate of calcium and magnesium, or a combination of these two minerals. Limestone contains a number of distinguishable natural characteristics, including calcite streaks or spots, fossils or shell formations, pit holes, reedy formations, open texture streaks, honeycomb formations, iron spots , travertine-like formations and grain formation changes. Most limestones are usually Grey, but all colors of limestone from white to black can be found.


Formation:

Limestones are usually formed over several years at the bottom of oceans or lakes from the accumulation of shells, bones and other calcium rich goods. Many aquatic organisms such as oysters, clams, snails, corals, and sea urchins draw calcium carbonate out of the water and use it to make their shells and bones. When these animals die the shells and bones are broken up by waves into shell, coral sand and mud.
If a limestone is subjected to intense heat or pressure for many years, a crystallization will occur and the limestone will become a "true marble". Chemically both of them are still Calcium Carbonate (TUMS), but the marble will have a crystalline structure and the limestone will have relatively flat appearance. Limestone that have magnesium in them are called"dolomitic limestones" and are typically much harder and more resistant to weathering. Limestones that will take a polish are considered marbles by most people, but technically, if there are still shells visible or the structure is not crystalline, it is still a limestone.

Features: *Texture varies from coarse to fine.
* Deposits are frequently of great thickness.
* Used as a flux in the extraction of iron
* Important varieties of limestone - marl, chalk, iolite, travertine, dolomite, and marble.


Basic Facts about Limestone:

GROUP TYPE: Sedimentary

COMMON MINERAL GROUP : Calcareous

COMPOSITION : Calcium Carbonate/ double carbonate of Calcium and Magnesium (Dolomite). Contains a variety of other minerals
such as silica, pyrite, iron oxides, clay, bituminous matter from organic materials.

POROSITY : 0.6 - 31.0 %

ABSORPTION : 0.2 - 12.0 %

WEATHERING EFFECTS : It depends on the type of limestone used, location, surrounding environment. But limestone surfaces in any
climate may weather irregularly due to the mineral composition of the stone.
TENDENCIES: Absorbs oils and other liquids, softer types are low scratch resistance, acid sensitive, some have big pores.

COLOR TYPE : Usually Grey-but any color type are found.

FINISHING : Some limestones can not be polished but other than that any type of finish is possible on them.
Please remember: As most limestones are highly absorbent, treat them with water or oil repellent. It is better to use a treatment product meant particularly for limestones. Also over time some rough areas might develop on the stone surface which is not a decay but a natural patina. Your local NSRA member could alter the surface to your satisfaction and also use the correct or correct combination of sealers to repel most liquids, give you the time need to clean the areas before any damage could occur.