Bismuth, element 83 on the periodic table forms beautiful, rainbow colored crystals. The color is due to a thin layer of Bismuth Oxide that forms on the surface of the crystal as it cools. Thinner oxide layers result in purple and blue, while thicker layers produce green, gold and red. Bismuth crystals grow in an odd stairstep shape because their edges grow at a faster rate than their faces.   Interesting Information: Once thought to be the heaviest stable element, Bismuth has been shown to be slightly radioactive, with a half-life approximately a billion times longer than the age of the universe (far less than enough to be harmful !). It is non-toxic and has numerous medical uses, including its use as the active ingredient in Pepto-Bismol.