Porosity
	Porosity is the parameter describing the amount of open space in a geologic material. Porosity is either presented as a fraction (0 to 1.0) or a percentage (0 to 100) of open space. All hydrologic equations use porosity as a fraction and conversions may be necessary.
		1. Sediment porosity consists of the open space between sediment grains. A well-sorted sediment has primarily one size sediment and will typically have higher porosities than poorly sorted sediments. Poorly sorted sediments have a wide range of sediment sizes and the small sized sediments can infill pore spaces.
			Well-sorted sand or gravel	25 to 50% porosity
			Silt	35 to 50% porosity
			Clay	30 to 60% porosity
		2. Sedimentary rocks undergo compaction which typically rearranges the sediment grains to reduce pore volume. Deposition of calcite or silica cements further infills pore spaces. The primary porosity is the open pore spaces left after lithification. After the rock is formed, forces can fracture the rock leaving open cracks or fractures. These fractures are called secondary porosity and can significantly increase open space within rocks.
		3. Crystalline rocks have low primary porosities due to interlocking mineral crystals. Secondary porosity from fracturing and weathering of the rock can greatly increase porosities.