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What are primary porosity and secondary porosity? Primary porosity is the porosity that remains after sediments have been compacted but have not been changed by subsequent chemical action or water flow through them. Secondary porosity is the additional porosity created by subsequent changes in sediments — especially such changes as fissures, fractures, solution vugs, and porosity resulting from dolomitization. Many rocks have small amounts of pore space in the form of isolated microcracks. It is useful to look at this as a characteristic of the skeleton and to reserve the term porosity for interconnected space capable of supporting fluid flow.