Final answer:
Porosity refers to the open spaces within a rock and is expressed as a percentage of open space to the total volume of the rock. Primary porosity is inherent in the rock's formation, while secondary porosity develops through geological processes after the rock's formation. Examples include sandstone for primary porosity and limestone with fissures for secondary porosity.
Step-by-step explanation:
Porosity is the measure of the open or void space within the rock and is crucial because it determines the capacity of the rock to hold groundwater. Porosity is expressed as a percentage representing the volume of open space compared to the total rock volume. Sedimentary rocks with well-sorted grains often exhibit high porosity due to the spaces between the grains.
Primary and secondary porosity are the two types of porosity found in geological materials. Primary porosity refers to the original pore spaces within a rock that is a result of its formation process. An example of high primary porosity would be sandstone, which has significant spaces between the grains of sand it is composed of. Secondary porosity, on the other hand, develops after the rock has formed, usually due to processes such as fracturing, faulting, or dissolution. An example of secondary porosity is the creation of fissures or caves in limestone due to the dissolving action of water.