Based on your picture, your sink is a "Swanstone 9" Deep Double-Bowl Granite Undermount Kitchen Sink - Nero" or one of its closely competing products. If it is this model you should call the manufacturer right away because "Swanstone offers an outstanding limited lifetime warranty on residential applications, and a limited 10 year warranty on commercial applications. For added convenience, choose from a variety of unique finishes to suit your kitchen." This is a quote form a web site that promotes the product. Here is the link:
Westside Wholesale, Inc. - Swanstone 9" Deep Double-Bowl Granite Undermount Kitchen Sink - Nero.
It appears that the surface has been stripped of its protective coaitng or patina. This happens with porcelain and some other man made surfaces. There are kitchen and bath restoration companies that specialize it reapplying a durable, high quality, translucent color matched coating to the surface. I've seen this type of damage repaired in this manner. Good Luck.