The Porosity Of Stone: Why Is Stone Porous?

What comes to mind when you think of stone? Well, most people would say, it’s hard, impenetrable, solid, unbreakable, etc., etc., but that really isn’t the case, as stone has attributes that make it a lot less solid than what many picture in their minds.

Actually, the structure of stone is such that it is not a concentrated mass, and it does have a certain rate of absorption. Observing a stone, with the use of a microscope, reveals that it contains innumerable tiny pores or cavities and there is a process involved in the formation of stone material that reveals the porosity of it.


Stone is formed through actions that involve the compressing of small particles or grains of matter and by re-crystallization in which both high heat and pressure rearrange the components of the stone. When these processes are occurring, small spaces remain between the particles and crystals, and these spaces are pores, and are the cause of a stone being porus.

In plain language, this simply means that natural stone countertops and tile floors have a certain rate of absorption. They can absorb most anything wet, such as water, liquids of different kinds and debris, particularly if natural stone countertops or floors are not secured with a protective sealant of some kind.

Stone Types and Porosity

Different types of stone have high and low porosity, which relates to the ratio of the small pores or spaces to the total volume of the stone. For example, granite is an igneous (molten/magma) type of stone with limited porosity, which is due to the way the stone was formed through pressure and heat. When it cools, cracking occurs and the stone exhibits fracturing more than it does porosity. In contrast, metamorphic stones, like marble and slate, have higher porosity because of the re-crystallization process. The crystals within the stone spread out and arrange themselves, which causes pores to materialize amidst the grainy material of the stone. Sedimentary stones, like travertine and limestone, have high rates of porosity that are caused by pressure that produces inseparability or cementation. This results in large voids in the stone’s formation, which means that any countertop or flooring choices with this type of stone should be cautiously considered.

  • Granite has a porosity ratio of between 0.4% – 1.5%
  • Marble has a porosity ratio of between 0.5% – 2%
  • Slate has a porosity ratio of between 0.4% – 5%
  • Limestone has a porosity ratio of between 0.6% – 31%


Permeability is another aspect connected to a stone’s porosity. It indicates transmission of fluids and is connected to the pore structure within the different stone types. Both porosity and permeability levels will determine the absorbency rate of a particular stone, and this is important when determining whether a stone surface is susceptible to stains, water marks and any other elements. When a stones surface is honed or matte in appearance, it is more likely to take in liquids because of its surface pores and openings, while polished surfaces have more limited absorption because of the vitrification process. The process blocks the pores on the surface and decreases absorption.

The porosity and permeability of stone are important features that homeowners should consider when choosing natural and engineered stone materials. If you need further information about either one of these basic concepts concerning stone, complete the online contact form and a representative will get back to you with the explanations you need to make a stone selection that meets your needs.