Visit the Gemological Institute of America website.Once there, you will see options to see pictures of "polished" or "rough" stones. Each option has different stone types available. Some of the stones listed are Emerald, Amethyst, Peridot, Tanzanite, Jade, Moonstone, Rose Quartz, Sapphire, and Opal.
Visit Rock Tumbler website.They have a terrific chart available to view, share, or print. Some of the stones identifyable are Amazonite, Malachite, Tiger Eye, Banded Amethyst, Orange Quartz, Onyx, and Various types of Agate.