Yes
Like marble, polished limestone is highly susceptible to surface changes or damage from kitchen acids including citrus juices, vinegars, mustards, and so forth. Unsealed, some of the more porous limestones can be subject to stains. Usually, no evidence remains once the liquid is removed and the granite dries. A stone sealer is highly recommended for all granite after installation. Some stones are more porous than others, so it is important to use a penetrating sealer to prevent stains from oil, wine or other liquids from soaking into the surface. Given that marble is more susceptible to staining by many foods, spilled liquids and other household materials, we do not recommend their use for kitchen countertops. Softer and more porous than granite, marble is more suitable for less-trafficked, formal areas. Born from molten magma, granite is a much more durable and functional stone than marble. Granite's crystalline structure is far more resistant to abrasions, staining and discoloration than most marbles. The choice between marble and granite depends on the aesthetic effects you want to achieve and how much use or abuse the stone will be subjected to. Although both are natural stones and quarried from the earth, granite and marble (and marble's relatives-limestone, onyx and travertine) are very different from each other. Born from molten magma, granite is a much more durable and functional stone than marble. Granite's crystalline structure is far more resistant to abrasions, staining and discoloration than most marbles. If you opt for a finish other than a polished finish, the surface porosity increases. The honed finish granite countertop is polished to a smooth surface but not enough to produce a reflective surface resulting in a more subtle, natural looking stone appearance. This finish will be more porous than polished. Resources. “Granite countertop Finishes from Wolf Granite.” Wolf Granite. Polished Granite Is the Most Durable. Most granite countertops are polished then sealed making them nearly impermeable. Polishing the stone creates a flat, smooth surface that reduces the porosity making it more resistance to spills and stains. The addition of a top-coat sealer helps to strengthen its endurance. All stone, even granite, is porous to some degree, and will absorb stains over time. Some stones are more porous than others, so it is important to use a penetrating sealer to prevent stains from oil, wine, or other liquids from soaking into the surface. Like marble, polished limestone is subject to surface changes or damage from kitchen acids including citrus juices, vinegars, mustards, and so forth. Unsealed, some of the more porous limestones can be subject to stains. Granite looks solid but it’s porous. Quartz is not — it’s non-porous. So you’ll need to seal a granite countertop but not a quartz countertop. It’s no big deal — it takes less than an hour once a year. Usually, a water-based penetrating (or impregnating) sealer does the trick.  Marble is a softer and more porous surface than granite or quartz so it can wear slightly. Part of marble’s charm is its changing luster as it ages, though it can always be re-polished and restored to its original shine. Marble typically requires sealant every year as well. Marble is a metamorphic rock composed of recrystallized limestone or carbonate minerals, such as calcite and dolomite. When these rocks are exposed to extreme temperature and pressure, the recrystallization process forces each molecule closer together and forms an interlocking carbonate crystal structure. (Redirected from Porous). Porosity or void fraction is a measure of the void (i.e., empty) spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0 and 100%. There are many ways to test porosity in a substance or part, such as industrial CT scanning. Marble and granite are examples of porous stone. Upkeep & Durability. The biggest difference in porous vs. non-porous surfaces is in the upkeep. While both types of counters can make a kitchen look good and work well, porous countertops simply require more upkeep. You will need to seal your natural stone countertops (like granite) at least once a year. Additionally, marble and limestone can be scratched more easily than harder stones such as granite. Marble is, however, sometimes used in the kitchen as a pastry slab; its perfectly smooth, cool surface is ideal for rolling out dough and piecrusts. Like marble, polished limestone is subject to surface changes or damage from kitchen acids including citrus juices, vinegars, mustards, and so forth. Unsealed, some of the more porous limestones can be subject to stains.
http://www.asgranite.com/FAQS.aspx http://www.asgranite.com/choose_stone.aspx http://www.asgranite.com/choose_stone.aspx http://www.sophisticatededge.com/are-granite-countertops-porous.html http://www.intertile.com/pages/stoneloc/stoneloc_3faqs.html http://news.nationalpost.com/homes/mike-holmes-rock-out-with-granite-countertops-and-others http://francinimarble.com/marble/ https://en.wikipedia.org/wiki/Porous http://info.leezasurfaces.com/blog/bid/95528/The-Best-Countertop-Options-Think-Non-Porous-Solid-Surfaces-Quartz http://www.intertile.com/pages/stoneloc/stoneloc_3faqs.html
is marble porous