It sounds like it needs polishing. Here's a link:
Use Polishing Powder
If your granite countertop's dullness is due to light, surface etching, granite-polishing powder may be able to remove it. The powder is slightly abrasive, so it removes shallow scratches, stains and other residue that might be causing the granite to look dull.
Hi Huma: To put a shine on your granite put a little cooking oil on a soft cleaning cloth and wipe it across the countertop. Buff it gently. This makes the counter a little bit stain-resistant and gives it a glossy shine. Even if you know how to clean countertops correctly your granite will need to be resealed periodically.
Here are some sites that should help you out:
Granite CPR is a good product!