Blue and green boulder Australian opal clasp

 "...For in them you shall see the living fire of the ruby, the glorious purple of the amethyst, the sea green of the emerald, all glittering together in an incredible mixture of light."

Pliny, 1st Century A.D.

A boulder opal is composed of a thin layer of opal, or intricated opal over an ironstone boulder.

It is a natural stone, not manufactured/lab made, and not a douplet, nor a triplet.

Most opals were formed in deeply weathered rocks in arid regions. During high rainfall periods, small amounts of silica were dissolved by water.

As the water evaporated, the remaining silica formed the spherical spheres, which create the myriad of colors that the opal displays, to give the opal its unique beauty of radiant color.