An alternative theory to groovy shamanic practices could lay in the practice of Geophagy or Pica.
There's anarticle on the subject here. http://www.tc.umn.edu/~call0031/pica.html
Interestingly the article also mentions Elfstenar which means that Mr Stonelifter may not be totally off the chart with his beautiful, though probably natural, elfenmarks.
cheers
fitz