Why is coquina classified as organic rock with a granular texture?

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Coquinas are type of sedimentary rocks that are formed from various parts and fragments of shells that come from animals like molluscs, brachiopods, and other invertebrates. The sedimentation may either be mixed with other substances or fully composed of shell fragments for them to be classified as coquinas.  The particles involved should also be at least 2mm in size to warrant a coquina classification.  With the seemingly big shell-like particles formed to become a rock, the texture is also expected to be rough and granular.  With its big particles and animal-shell origin, coquinas are officially classified as organic types of rocks that have a granular texture.

Most coquinas are formed near shore lines wherein the waves are pretty violent and strong. The strong force from the water causes the abrasion and formation of shells leading to the sedimentation process. The formation of coquinas may depend on natural conditions and its texture and hardness may either be poorly cemented and extremely granular with some rock formed with a strong bond and a smooth granular surface. Softly-cemented sedimentations are classified as grainstones and are easily crushed with minimal force.  Rocks that are considered well-cemented tend to be stronger in terms of the bonding in the shell particles.  The texture of these stronger coquinas is also smoother and they are classified as biosparites.

Coquinas had been used for building in construction in the past.  Whether the stones are well-cemented or soft, they can be useful in making walls and small buildings.  The good thing about coquinas is that they can be sourced easily since these rocks are soft enough for easy quarrying.  In the past, coquinas were not thought of as essential for building and construction because of their very soft and granulated texture.  People eventually realized though that they can make the stones strong enough for building just by drying them off under the sunlight for a few years.  It takes about 1 year to 3 years for coquinas to fully harden and render themselves useful in creating posts and walls for various buildings.

Author: erwin

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