Granite: Non-Reactive Natural Stone...

All Granite is volcanic (igneous) rock that was formed in and by the heat.  It consists of mostly silicates including Quartz and Mica with mineral imperfections that give it it's widely varied appearance.  It is a very stable material and stands up well to most abuse.  The polish on granite is from grinding not from an applied finish.  There is nothing to wear off the surface.  It is sealed with a silicone penetrating sealer.  Re-sealing is not necessary.  The only caution is that you must not refrain from using solvents on it (like finger polish remover) as this may remove the sealer.  Mold and mildew should not be an issue.  Other than that, cleaning with Windex, antibacterial sprays, etc is the best way to keep it clean.  While the surface of these materials can be worked the basics of the natural stone cannot be altered in fabrication.

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