OK I've done some googleing on it and here's a pic i found comparing Carib Sea and playsand found at your local Home Depot, Wal-Mart or Toys R Us:
http://www.planetkc.com/irobot/BrainBase/OolithicComparison/wf_OolithicSands.jpg
*note CS=Carib Sea, SD=Southdown/YardRight/Old Castle Stone...