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Opal

Opal

Hydrated silica with possible play-of-color

Black Multicolor Orange White
Optical properties

Optical characteristics

Ref. index
1.37 – 1.47
Luster
Vitreous to waxy
Pleochroism
Variable Variable depending on transparency, orientation, and variety.
Fluorescence
Variable to inert.
Origins

Source localities

Australia Australia: Lightning Ridge
Legendary ★ Top Source

Lightning Ridge in New South Wales is the exclusive source of black opal, the most valuable opal type, with dark body tone and vivid play-of-color.

25% est. supply
Australia Australia: Queensland opal fields
Premium ★ Top Source

Australia is the dominant global source for precious opal, producing the widest range of types including crystal and white opal.

45% est. supply
Ethiopia Ethiopia: Wollo / Shakiso / emerald fields
Notable ★ Top Source

Ethiopia's Welo (Wollo) region has emerged since 2008 as a major source of hydrophane opal with exceptional play-of-color.

20% est. supply
Mexico Mexico: Querétaro / Jalisco / Sonora / Coahuila
Notable

Mexico is the primary source of fire opal, a transparent orange to red opal prized for its body color rather than play-of-color.

10% est. supply
Treatments

Enhancement & treatment

Color Enhancement Smoke Treatment Smoke treatment darkens opal body color to imitate black opal or improve contrast. It… Color Enhancement Sugar-Acid Treatment, Opal Sugar and acid create carbon inside porous opal to darken the body. It can… Assembled Assembled Stones, Doublets and Triplets Assembled stones combine separate materials to imitate a single gem or enhance appearance. They…
Inclusions

Inclusions & features

Crystals Crystal Inclusions Under 10x loupe: solid, well-formed mineral crystals trapped inside the host gem. They may… Fractures Feathers and Fractures Under 10x loupe: irregular internal surfaces that catch light and appear bright, wing-like, or… Fractures Fingerprint Inclusions Under 10x loupe: curved or wavy lines of tiny dots forming patterns that look… Clouds Pinpoint Clouds Under 10x loupe: concentrations of extremely tiny bright dots that individually are too small… Multiphase Two-Phase Inclusions Under 10x loupe: a transparent irregular cavity containing both a liquid phase and a…
Identification

Instruments used

Dichroscope Reveals pleochroism, instantly eliminates singly-refractive stones Hydrostatic Scale Measures specific gravity, works even on opaque stones 10x Loupe Your most-used instrument, start every examination here Polariscope Determines single vs. double refraction, quick and conclusive Refractometer Measures refractive index, the backbone of gem identification UV Lamp, Long Wave and Short Wave Fluorescence exposes treatments, synthetics, and origin