How Does Opal Acquire its Unique Coloring?

What Exactly is Opal?

Technically speaking, opals are a form of silica, except that they are non-crystalline. Belonging in the quartz and agate family, opal still has differences from these two stones. Opals are thought of as precious stones for one, right alongside diamonds, emeralds, sapphires, and rubies.

How Opals are Created

Naturally, opals are made out of a solution of silicon dioxide and water. The latter soaks sandstone while picking up some particles of silica. Over millions of years, the solutions stayed in the voids and caused the rock to be solidified, giving us the precious opal.

The unique color of opal has to do with the water being lost from the silica solution. This then caused it to become a gel, with the silica forming spheres inside it. The latter are uniformly sized and packed together to form a pattern. Light passes through them because they are hollow and round.