An opal begins its life as water, trickling down through gaps in soil and rock. Water flows through sandstone, limestone, and other layers of the crust picking up a microscopic compound called silicon dioxide.
This silica enriched liquid then enters the empty spaces or voids inside pieces of volcanic rocks, prehistoric river beds, and even bones of primitive creatures. It gradually evaporates leaving behind the sicilia particles that organise themselves to form a gel.Inside this gel millions of silica atoms form a series of concentric shells layer by layer. The gel ultimately hardens as a glass like material. Majority of the time the structure of silica is haphazard, resulting in formation of common opals; however, the tiny percentage that comes under precious opals have regions where silica beads of uniform size are orderly arranged. The differences in the arrangement of the silica gel lattices within a particular stone results in the wide range of colour patterns in opals.
The circumstances necessary for the formation of these stones are so uncommon that they only occur in a handful of places. About 95% of all opals come from Australia.
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