Tumbled naturally by river water.  They are said to offer access to ancient wisdom and cultures, may be programmed to tune into a specific age or culture, especially as amethyst and smoky quartz stones.  Addresses fluid imbalances, hormones, water retention, kidneys, blood circulation.  Keeps you from oversentimentality, curbs an addiction to fortune tellers and messages from the spirit world. 
 
Natural Seer Stones are tumed in the Ema River in southern Brazil; also known as Ema's Eggs, after the river and because their uncut white shell resembles an egg. When these frosted stones are cut, and one end polished by a lapidarist, their windows reveal other worlds.