Boulder Opals

Boulder opal is found only in an area of eastern Australia, between the New South Wales border and northwest Queensland. It is highly prized for its array of iridescent color--flashes of green, blue, aqua and sometimes yellowish or red colors which are referred to as "fire".

Millions of years ago, boulder opals were formed when silica from decomposing rocks mixed with ground water and filled in cracks and crevices of brown ironstone boulders. Over time, the silica layers hardened. Now, the deposited layers of silica particles cause light to diffract like miniature prisms, creating bright flashes of color when struck by light from different angles.