Fire Opal
| Also known as | Opal (Opal family) |
|---|---|
| Colour | Orange, Red |
| Mohs hardness | 5.5–6 |
| Lustre | Subvitreous to waxy |
| Streak | White |
| Crystal system | Amorphous |
| Transparency | opaque, translucent, transparent |
| Cleavage | None |
| Fracture | Conchoidal to uneven |
| Chemical formula | Hydrated silica. SiO 2 ·nH 2 O |
| Specific gravity | 2.15 |
What is Fire Opal?
Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.
How to identify Fire Opal
- Lustre: Subvitreous to waxy.
- Hardness: Mohs 5.5–6 — about as hard as a steel knife.
- Streak: White.
- Habit: Amorphous crystal system.
Fire Opal value
Fire Opal is a fine gemstone priced per carat by quality — colour, clarity, cut, carat and origin — not by weight in grams. Typical market ranges:
| Quality | Price per carat |
|---|---|
| Commercial | $10–$50 / ct |
| Good | $50–$200 / ct |
| Fine | $115–$600 / ct |
| Top | $300–$2,000 / ct |
Ranges cross-validated across two independent research passes against gemstone price guides, 2026-06 — sources: gemrockauctions.com, opalauctions.com. Colour saturation, clarity, cut and origin move the price enormously, and treatments or lab-grown stones sell for a fraction — so this is a guide, not an appraisal. Have anything valuable checked by a certified gemmologist. See the full crystal & gemstone value guide.
