Queensland Blue-Green-Yellow Freeform Boulder Opal

About Boulder Opal

Boulder opal is a natural opal formed within, and usually attached to, dark ironstone. Its body colour may be grey, brown, reddish brown or nearly black, with patches or veins of blue, green, yellow, orange and red play-of-colour. This shifting spectral effect comes from the orderly arrangement of tiny silica spheres, which diffract light. The opal itself is translucent to opaque, while the ironstone matrix is opaque. Opal is…