UBATUBA

Hello, I just had my kitchen counters done with Ubatuba granite and it was supposedly from a piece that was left over in their yard. After they left I noticed a large solid black spot -- it almost looks like someone used a paint brush on it. I can still see "sparkles" coming thru. The granite people told me this is a normal "flaw" in the material. Is this correct? Also, how do I clean this product? From what I've read I guess I should not be using ordinary detergent. Also do I need to seal this product. thanks kbroph