Hi there,

shell microstructures have various patterns if you notice it closely. The first image shows the porosity nature and the next two like small craters. Are the images from the outer layer or inner layer of the shell??

best

Deepak

thank you for your answer, the images are outer layers.

This is likely eroded complex crossed-lamellar microstructure.  You can see comparable shell dissolution in the bivalve Corbicula fluminea (see for example Prezant et al. 1988).  The lamels composing the crossed-lamellar structures breakdown under conditions that induce long term adduction of the valves; this can produce a decrease in pallial fluid pH and thus the erosion and lack of crystalline structure (and pitting) seen in your images. Venerid bivalves do not have nacre.  For a review on venerid shell microstructure see: Shimamoto (1986).  

Thank you very much for your good answer, and i need one more clarification if there is any possibility for homogeneous microstructure with porous layer.

There are different types of "homogeneous" microstructures...some appear to be actual depositions (i.e. the microstructures are a defined calcareous layer) but others could be remnants of other eroded (or otherwise altered) microstructures.  The images you shared do not appear to be of a homogeneous nature.  

Thank you for the answer, i cleared myself.