Bismuth Crystal

A few days ago a purchased a bismuth crystal off of eBay for pretty cheap.  Bismuth is a grey metal with a few interesting properties.  In addition to being the active ingredient in Pepto Bismol, when it is cooled slowly, it forms square spirals in a stair-stepped shape.  During this process, it forms an oxide layer that causes interference  with reflected light giving it an a rainbow effect on the surface.  As far as buying your own crystals, the red and yellow hues are less common and generally command a higher price.  For comparison, the crustal shown below is about 2" long and cost ~$15. I did not purchase from but they do have some of the nicest ones that I've seen for sale.  Click on the read more link for photos.