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Opal · Variety of Opal

Fire Opal

Transparent to translucent orange to red opal

Orange Red Yellow
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

Brazil Brazil: Minas Gerais / Paraíba / Bahia
Major

Major source for beryl, tourmaline, quartz, topaz, chrysoberyl and rare minerals.

10.5% est. supply
Ethiopia Ethiopia: Wollo / Shakiso / emerald fields
Major

Major modern source for opal and emerald.

15.8% est. supply
Mexico Mexico: Querétaro / Jalisco / Sonora / Coahuila
Notable

Known for fire opal, turquoise, amber and collector minerals.

73.7% 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