The beginning of opal formation lies deep within the earth and starts with one of the most basic elements - water. This water, enriched with silicon dioxide, also known as silica (H₄SiO₄), slowly penetrates into the cracks and cavities of the rock. When rainwater flows over rocks and soils that are rich in silicon dioxide, it absorbs this silicon dioxide in the form of silica. The cracks are caused by tectonic movements in which the earth's plates are shifted and broken up. The silica-containing water collects in these cavities and forms the basis for the later formation of opal. Incidentally, we find silica in plants, lakes and even in cosmetic products and as a food supplement.

As the water gradually evaporates, the silica remains behind. This silica initially forms a gel that completely fills the cracks and cavities in the rock. Over millions of years, this gel solidifies under the influence of pressure and temperature changes.

The conditions for the formation of opals vary considerably from region to region and have a significant influence on the properties of the gemstone. Australian opals, which are the most famous and sought-after in the world, are often formed in desert regions where evaporation plays a crucial role. The dry climate of these areas favours the process of silica deposition, which is how the typical, intense play of colours of Australian opals develop.

In other parts of the world, such as Ethiopia, the geological conditions are different, resulting in opals with unique characteristics. Ethiopian opals, often known as Welo opals, are characterized by their vibrant colors and transparency, which are rarely found in Australian opals. The differences in mineral composition and climatic conditions at each location give opals from different regions their individual characteristics, making each stone a unique natural wonder.

Click here to find out the main opal types and their origin.

And click here if you want to learn more about opal mining techniques.