Bismuth is a brittle metal with a white, sliver-pink hue. Bismuth often occurs in its native form, with an iridescent oxide tarnish reflecting many colours from yellow to blue. The spiral, stair-stepped structure of Bismuth crystals is the result of a higher growth rate around the outside than on the inside edges.
Variations in thickness of the oxide layer, which forms on the crystal surface causes different wavelengths of light to interfere upon reflection. This displays a rainbow of colours.