A look at Technical Classification of Limestone
Posted on Jun 2, 2015
Limestone is a sedimentary rock that is formed from the skeletal fragments of the ancient marine organisms. Corals or foraminifera are the major contributors of natural limestone slabs. The limestone slabs are part of the carbonate rocks made of calcium. The Indian limestone slabs are formed from a distinct category of carbonate grains. Apart from corals, the Indian limestone slabs also showcase the blending of skeletal fragments of Ooids, Intraclasts, Peloids and Extraclasts.
The Indian limestone slabs are made of aragonite and calcite secreted by the marine organisms. They are available in the form of shells which solidify into plates and slabs once the organisms die out.
When it comes to impurity, the Indian limestone slabs have the least amount of silica and sand content. It is usually accompanied with other forms of silica like flint, jasper and chalcedony. Indian limestone slabs are free from the siliceous micro-skeletal remains of sponges, spicules, diatoms and radiolarians. Most varieties of the Indian limestone slabs have a variable amount of clay, silt and terrestrial detritus, depending on the location from where they are excavated and mined.
Presence of a river bed system has a major effect on the amount of impurities present in the limestone blocks. Another family of Indian limestone slabs is derived from the chemical precipitation of ground water in caves. Travertine varieties of the limestone slabs are considered as the commercially viable range in the category of natural stones. It has a healthy blend of calcite and aragonite. They rise or fall from the caves as stalagmites and stalactites. Apart from river beds and caves, Indian limestone slabs are also formed as part of an evaporate environment with deposits spread over a lacustrine system.
Indian limestone slabs are classified as per two accepted schemes. They are used to classify all carbonate rock forms and stones. The classification schemes are:
– Folk Classification
– Dunham Classification
Folk classification is based on the granular composition of the limestone slabs. It also places significant emphasis on the interstitial material present in the limestone. Folk Classification gives rise to three major components present in the composition of the Indian limestone slabs. They are:
– Allochems or Grains
– Matric of micrite
– Cement made of sparite
The Indian limestone slabs classified as in Folk Scheme is used during the inspection of samples using petrographic microscope.
When it comes to classifying the limestone samples under Dunham scheme, the depositional textures are studied. The name of each Indian limestone slab is derived from the texture of the grains displaying a distinct depositional fabric. Apart from limestone, Dunham classification is used in other rocks. Limestone family can be classified into four main groups. All of them are based on the relative amount of Clastic impurities present in the sample as coarse or fine particles.
Dunham scheme of classification is more popular and is widely used by the exporters of Indian limestone slabs as it deals with the porosity of the rocks unlike in Folk Classification. It is based on fabric texture and not on the grains appearing in the sample.