Opal

Iridescent opal occurring in ironstone matrix from Australia, displaying vivid play-of-color with flashes of green, blue, and violet distributed along fractures and intergranular zones of the host rock. The opal occurs as thin seams and patches rather than discrete crystals, which is typical for sedimentary opal deposits.

Australian opal formed by low-temperature silica-rich fluids percolating through porous or fractured host rocks, where amorphous silica gel precipitated and later solidified into opal. The distinctive play-of-color is caused by the regular arrangement of submicroscopic silica spheres, producing diffraction of light.

The ironstone matrix indicates formation in an oxidized near-surface environment, commonly associated with weathering profiles and ancient sedimentary basins. Such matrix-hosted opals are characteristic of several Australian opal fields and are appreciated for their natural, uncut presentation.

This specimen is valued primarily as a natural matrix opal, emphasizing geological context rather than gem cutting potential. The vivid color contrast between the earthy host rock and the iridescent opal enhances its aesthetic and educational appeal.