The Secret of Opal Colours
The secret of the colours
Why opal has colours ? Also why each stone has different colours and patterns ?
We already know that opal is made from silica combined with water. Some other components have been found inside opal, but we think these other components will just make it complicated in explaining.
Opal is a non-crystalline form of the mineral silica and is formed from amorphous "balls" or "lumps" of silica. So the opal is a very unique gem compared with others, like diamonds or a ruby which is formed crystalline. This is the reason why variation of colours are in opals.
When you were in school, you probably learn about triangular Prisms. Do you remember ? The tiny balls of silica in opal are working like "Prisms". The vast number of colours in opals are caused by the regular array of silica balls diffracting white light, and breaking the light into the colours of the light spectrum. The actual range of colour in a particular Opal is determined by the diameter and spacing of its silica balls (refer to figure below).
cr: Black and Boulder Gemstory
cr: Presti and Presti Lapidary