Oval Oregon fire opal cabochon (USA), 10×8 mm. Translucent amber orange with depth effect when backlit. Flat back. Compact format ideal for earrings. Unique piece selected at a wholesale lapidary market.
Piece details
| Mineral |
Fire opal (SiO₂·nH₂O, hydrated opal) |
| Dimensions |
10×8 mm, approx. 4–5 mm height. Variation of ±0.2 mm. |
| Shape and back |
Oval, flat back |
| Finish |
Mirror polish |
| Hardness |
5.5–6 Mohs — we recommend a closed bezel setting to protect the edge |
| Origin |
Oregon, USA |
| Treatment |
Untreated |
| Type of piece |
Unique piece |
This specific piece
The 10×8 mm is the intermediate size for fire opal: small enough for a stud earring with presence, large enough for the translucent orange to be visible and impactful. At this size, the backlighting effect — the intensification of color when light passes through the gem from back to front — is perfectly visible under normal indoor lighting conditions.
The tone of this specimen is a warm amber orange, deeper than vivid orange, leaning towards toasted caramel. The translucency is uniform with no pockets of opacity, indicating good internal material quality. Oregon fire opal in this format is often chosen by jewelers looking for the impact of orange without the overwhelming presence of a large format.
How fire opal forms
Opal is hydrated silica (SiO₂·nH₂O) with an amorphous structure. The orange color of fire opal comes from traces of iron oxides incorporated during deposition in volcanic cavities. The Oregon deposits are located in rhyolitic formations of extinct volcanoes, where silica circulated in aqueous solution for millions of years. The water content (between 3% and 21%) directly influences translucency: higher retained water content means greater translucency. Unlike precious opal — which shows play-of-color due to its layered silica sphere structure — ordinary fire opal is amorphous without that microstructure, hence it has body color without the iridescent effect.
What mounting it works for
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Bezel setting (925 silver) — recommended. The bezel protects the opal's perimeter from accidental knocks; especially important for earrings, which can hit against the jaw or neck.
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Stud earrings — 10×8 mm is an ideal size for an elegant stud: present but not exaggerated, with enough orange to be the star.
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Wire wrap — viable with thin wire; handle lateral pressure on the gem carefully.
Fire opal in lapidary tradition
Fire opal was valued in Mesoamerica even before the conquest. The Aztecs called it vitzitziltecpal and associated it with fire and transformation.
In crystal tradition, fire opal is linked to energy and spontaneous action. The symbolic properties attributed to minerals belong to cultural and historical traditions. They are shared for educational purposes, not as medical advice or a substitute for professional care.
How to recognize genuine fire opal
The orange of genuine opal changes subtly with lighting — more intense with backlighting, softer with side lighting. Orange glass has a uniform, flat color that does not respond to the direction of light in the same way. Opal is lighter than glass of the same size. Under magnification, it may show internal curvilinear microfissures (crazing) characteristic of hydrated silica, which are a natural structure.
Frequently asked questions
What is the difference with the 14×10mm fire opal in the catalog?
Only the size. The mineral, origin, and optical properties are identical. The 10×8 mm is more suitable for earrings and compact pendants; the 14×10 mm for larger centerpieces with more presence.
Does this opal have play-of-color?
No. It is body color fire opal — translucent orange without the multi-colored iridescent effect of precious opal. They are distinct varieties.
Is it treated?
Untreated. The orange is the natural color of the material — iron oxides in the silica.
See also: cabochons collection · silversmithing · wire wrap.
