I would contact a granite countertop company and ask them or a company that deals with granite.Granite counter tops have to be sealed at least twice a year other wise they are suject to staining.For example if one spills orange juice on the counter top and doesn't wipe it up immediately it will cause a permanent stain.
I use Lemon oil for about anything that is hard to shine.
I am sure it will give it a shine
This company in Sarasota is so helpful on granite. Give them a call http://www.stonetrend.com/
They can tell you exactly what to do and how to take care of your counters properly.
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