Granite |
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Granites are made up of several different minerals, each mineral having a different hardness. Granites can contain feldspars, biotites, amphiboles, Fe-Ti oxides, and other mineral combinations. On the Mohs scale, diamonds are the hardest substance with a hardness of 10. Felspars have a hardness of 6.5 to 7 and are very durable. The biotites (the black minerals throughout the slab) on the other hand, are very msoft (2.5) and are flaky. All true granites have biotite in their composition. Because biotites are soft and flaky, the first few layerrs are removed during the polishing process, causing pits throughout the slab. Some granites have more biotite throughout their composition than others. The higher the biotite composition of the stone, the more pits it will have. All polished igneous/metamorphic rock will have varying degrees of pits, depending on the amount of biotites, muscovite, and philogopite.
The "pits" do not make granite less durable or inferior. One must understand that pits are in all granites and should be excepted when dealing with natural, polished stone containing several types of minerals with different hardness.