A granite floor is impervious to most things but does benefit from regular cleaning.
There are several things to remember when cleaning a granite floor:
Do Not Let Spills Sit
Mop up liquids as quickly as possible.
A Damp Mop Is Enough
Use a damp mop (water only) to clean your floor on a regular basis.
Do not use an abrasive cleaner, this will scratch the surface and make matters worse
Do not use commercial floor cleaners unless they are specifically marked as safe with granite floors.
If you have rugs on your granite floor make sure they are suitable and don’t allow dirt to be trapped underneath them—this will damage the surface.
Detergent for Stubborn Marks
If a damp mop will not remove some marks, try a Ph neutral detergent rather than soap.
Often the worst marks on a granite floor are caused by the cleaning agents not being dried off properly so whenever you are cleaning the floor make sure to dry it thoroughly.
If your granite floor refuses to be cleaned to your satisfaction by normal means, you might have to have the granite re-finished professionally. If you do, use a cleaner that is then designed to maintain your new granite floor finish.