All stones are absorbent and retain water to some degree. According to the Merriam-Webster Dictionary, a stone's ability to absorb water is called its "porosity." The term "permeability" refers to its ability to hold water. Knowing which types of stone absorb and retain the most water will prevent structural problems in your project later on.
Flagstone is a highly absorbent stone, but does not absorb deeply because of stone layering. Because of the layering, it does tend to retain water. To prevent absorption it must be heavily sealed. Flagstone is commonly used for paving, patios and different types of construction.
Limestone is deeply absorbent because of its soft texture. According to the Florida Geological Survey, limestone is very soluble, meaning water dissolves the stone over time. The longer limestone is exposed to the elements, the more porous it becomes. The Great Pyramid in Egypt is partially made of limestone.
Sandstone absorbs water so much that it is frequently used as a coaster. It absorbs and retains water effectively. It is also fairly inexpensive and easy to find. Sandstone is naturally available in many different colors, including black, buff and red.
Although not to the same degree as the other three types of stone, slate is still very absorbent. While limestone has a porosity ratio between 0.6 percent and 31 percent, slate has a ratio of between 0.4 percent and 5 percent, and does not retain water as much. Slate consists mainly of the mineral mica and is not suitable as a building material, though it was used as tiling for roofs in the past.