Approximately how many million years ago was most opal formed?

Most opal is believed to have formed during the time period of 15 to 30 million years ago, particularly associated with geological events in Australia, which is one of the primary sources of opal. During this timeframe, significant volcanic activity and sedimentation processes occurred, leading to the conditions necessary for opal formation.

Opal is a hydrated silica, formed from the deposition of silica from water, and its formation is heavily influenced by the environmental conditions of the time. The 15 to 30 million years ago period aligns with these geological processes, making this timeframe significant in the context of opal's geological history.

Understanding the geological formations and the conditions that allowed for opal to develop helps in appreciating its origins and the uniqueness of the stone. This context gives insight into the broader aspects of gem formation and the factors that influence mineral development over geological timescales.