RocksdayFire Agate vs Opal
To tell Fire Agate from Opal: Precious opal's color is in a pale or dark body as pinpoints, and opal is much softer.
Brown chalcedony layered with thin films of iron oxide that flash red, green and gold when the stone is tilted.
Photo: Maricopa Mining LLC, CC BY-SA 3.0
Hydrated silica with no crystal structure. In precious opal, stacked microscopic spheres split light into flashing rainbow patches.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Precious opal's color is in a pale or dark body as pinpoints, and opal is much softer.
Side by side
| Property | Fire Agate | Opal |
|---|---|---|
| Type | Mineral | Mineraloid |
| Mohs hardness | 6.5–7 | 5.5–6.5 |
| Luster | Vitreous to waxy | Vitreous to waxy |
| Streak | White | White |
| Colors | Brown, Orange, Red, Green | White, Black, Orange |
| Crystal system / structure | Microcrystalline quartz (chalcedony) | Amorphous |
| Specific gravity | 2.6–2.7 | 1.9–2.3 |
| Formula | SiO₂ | SiO₂·nH₂O |
| Found in | Slaughter Mountain, Arizona; Deer Creek, Arizona | Coober Pedy, Australia; Lightning Ridge, Australia |
Properties that are the same for both are grayed out.
How to identify fire agate
- Brown or orange body color with patches of iridescence.
- Waxy, and hard enough to scratch glass.
- The color sits in curved layers, not in round opal dots.
Crystal system: Microcrystalline quartz (chalcedony)
Full Fire Agate guide →How to identify opal
- Flashes of spectral color that shift as you turn it.
- Waxy to glassy luster.
- Light in weight for a gemstone.
- Common opal lacks color play and looks milky.
Structure: Amorphous
Full Opal guide →More comparisons
Frequently asked questions
What is the difference between fire agate and opal?
Fire Agate is a mineral (SiO₂) with a Mohs hardness of 6.5–7 and a vitreous to waxy luster, usually brown, orange, red or green. Opal is a mineraloid (SiO₂·nH₂O) with a Mohs hardness of 5.5–6.5 and a vitreous to waxy luster, usually white, black or orange.
How can you tell fire agate from opal?
Precious opal's color is in a pale or dark body as pinpoints, and opal is much softer.
Could you tell them apart from a blurry close-up?
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