Limestone is a sedimentary rock composed principally of calcium carbonate (calcite) or the double carbonate of calcium and magnesium (dolomite). It is commonly composed of tiny fossils, shell fragments and other fossilized debris. These fossils are frequently visible to the unaided eye on close examination of the stone surface, however this is not always the case. Some varieties of limestone have an extremely fine grain.
Limestone is usually gray, but it may also be white, yellow or brown. It is a soft rock and is easily scratched. It will effervesce readily in any common acid.
Limestones may vary greatly in texture and porosity from coquina, which is a matrix of whole or pieces of sea shells loosely cemented by calcite, to oolitic limestones and microcrystalline limestones whose structures are so fine that they can be seen only under magnification.
Limestone deposits can undergo metamorphism during major geological events resulting in a recrystallizing as marble.
Oolitic limestone consists of substantial amounts of “oolites” or “ooliths.” Oolites are small spherical or sub-spherical grains of concentric calcite.
The actual classification of limestones and marbles can be very confusing to the non-geologists. The same stone can be marketed one time as a limestone and, at another time and place, sold as marble. The subtleties which sometimes differentiate between grades and types of stones are frequently beyond the concern and expertise of maintenance workers, building managers and historical architects with responsibility for maintenance of the resources. While this is understandable, it does not lessen or eliminate the need to accurately identify the materials which must be treated and maintained. Failure to accurately identify a material to be treated can result in the failure to consider important technical details which subsequently results in irreversible damage to the resource(s).
Credit : GSA
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