OPAL

If a rainbow could be captured and set in a ring then it would be called opal. Chasing the rainbow (finding the colour layers that exist in the rough rocks) has been a pre-occupation of lapidaries for years. Opal is comprised of tiny spheres of silica. When these spheres are of uniform size and arranged in a three dimensional layer, light is diffracted into the colours of the spectrum and conveyed as a flash of coloured light. Opal also contains water, sometimes as much as 30%, so great care must be taken when heating the stone to avoid cracking. Over time the water in the opal can dry out and serious cracks can occur.