Comparison · Quartz Family vs Semi-Precious Stones
Fire Agate vs Opal
Fire Agate and Opal are easy to confuse. Fire Agate is harder (Mohs 7) than Opal (Mohs 5.5), so Fire Agate will scratch Opal and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Fire Agate and Opal
- Fire Agate is harder (Mohs 7) than Opal (Mohs 5.5), so Fire Agate will scratch Opal and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
- Luster is different: Fire Agate is waxy while Opal is vitreous.
- Fire Agate feels noticeably heavier for its size (specific gravity 2.6 versus 2.1 for Opal).
- Well-formed crystals give it away: Fire Agate is hexagonal, Opal is amorphous.
Fire Agate vs Opal properties
| Property | Fire Agate | Opal |
|---|---|---|
| Type | Quartz Family | Semi-Precious Stones |
| Mohs hardness | 7 | 5.5 |
| Luster | waxy | vitreous |
| Streak | White | White |
| Transparency | translucent | translucent |
| Specific gravity | 2.6 | 2.1 |
| Crystal system | hexagonal | amorphous |
| Common colors | Brown, Orange, Red, Gold, Iridescent | White, Black, Fire, Blue, Pink |
| Rarity | uncommon | uncommon |
| Typical specimen value | $15–$1000+ | $50–$10000+ |
Which is more valuable?
Opal is usually the more valuable of the two: a typical collector specimen runs about $500 against $90 for Fire Agate, and premium Opal can reach $10000 or more.
About Fire Agate
Fire Agate is an agate variety with iridescent internal color flashes, usually in warm brown, orange, red, and gold tones.
About Opal
Opal is famous for its play-of-color, caused by the diffraction of light through microscopic silica spheres. Australia produces 95% of the world's opals.
Fire Agate vs Opal FAQ
Is Fire Agate the same as Opal?
No. Fire Agate is a quartz family while Opal is a semi-precious stone. Fire Agate is harder (Mohs 7) than Opal (Mohs 5.5), so Fire Agate will scratch Opal and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
How can you tell Fire Agate from Opal?
Fire Agate is harder (Mohs 7) than Opal (Mohs 5.5), so Fire Agate will scratch Opal and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Luster is different: Fire Agate is waxy while Opal is vitreous. Fire Agate feels noticeably heavier for its size (specific gravity 2.6 versus 2.1 for Opal).
Which is harder, Fire Agate or Opal?
Fire Agate is harder: Mohs 7 against Mohs 5.5 for Opal.
Which is more valuable, Fire Agate or Opal?
Opal is usually the more valuable of the two: a typical collector specimen runs about $500 against $90 for Fire Agate, and premium Opal can reach $10000 or more.
