Fire opal

Quick facts

Formula

SiO2·nH2O

Hardness

5.5–6.5

Luster

vitreous to subvitreous, sometimes resinous

Colors

yellow to orange to red; may or may not show play-of-color

Fire opal is a warm yellow‑to‑red variety of common opal valued for its vivid body color and, in some stones, play‑of‑color. Much material comes from Mexico, and it is commonly cut as domed cabochons or freeforms.

Look for a uniform orange‑to‑red body with a vitreous to slightly resinous ‘wet’ glow, no visible banding, no cleavage, and glossy conchoidal chips; any spectral flashes elevate it from common opal to fire opal.