RocksdayAgate vs Onyx
How to tell them apart
Banded chalcedony — quartz made of microscopic crystals — that fills cavities in volcanic rock layer by layer. Light passes through the bands when held up to the sun.
Photo: James St. John, CC BY 2.0
Chalcedony with straight, parallel bands, classically black and white. Most solid black onyx is dyed.
Photo: W.carter, CC BY 4.0
Key differences
- Agate bands are usually curved and concentric.
Side by side
| Property | Agate | Onyx |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6.5–7 | 6.5–7 |
| Luster | Waxy to vitreous | Waxy to vitreous |
| Streak | White | White |
| Colors | Red, Orange, White, Gray, Brown, Blue | Black, White |
| Crystal system | Microcrystalline quartz (chalcedony) | Microcrystalline quartz (chalcedony) |
| Specific gravity | 2.58–2.64 | 2.58–2.64 |
| Formula | SiO₂ | SiO₂ |
| Found in | Lake Superior shores; Rio Grande do Sul, Brazil | Brazil; India |
Properties that are the same for both are grayed out.
How to identify agate
- Concentric or parallel bands, often in red, orange and white.
- Translucent at the edges when backlit.
- Waxy surface on rough, weathered pieces ('pitted' rind).
- Hard enough to scratch glass.
Crystal system: Microcrystalline quartz (chalcedony)
Full Agate guide →How to identify onyx
- Straight, parallel bands — not curved like most agate.
- Hard (scratches glass), waxy polish.
- Uniform jet-black stones are usually dyed chalcedony.
Crystal system: Microcrystalline quartz (chalcedony)
Full Onyx guide →More comparisons
Could you tell them apart from a blurry close-up?
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