What does porosity measure in geological terms?

Porosity is a crucial concept in geological terms that measures the volume of void spaces (or pores) within a material, such as soil or rock. Specifically, it quantifies the capacity of these materials to hold water or other fluids. When discussing porosity, one is interested in how much water can be stored in those pores; thus, option B accurately captures this definition.

Understanding porosity is essential for various applications, including groundwater management, reservoir engineering, and assessing soil health, as it directly relates to the material's ability to retain water. A high porosity indicates that a large volume of fluid can be stored within the rock or soil, making it significant in hydrological and environmental studies.

The other choices do not accurately represent the definition of porosity: the amount of sediment or mineral concentration concerns composition rather than the void space, and density relates to mass per unit volume rather than the capacity for water storage within those voids.