RocksdayAgate vs Chalcedony
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
Quartz made of microscopic fibers. Plain chalcedony is soft blue-gray and often grows in bubbly, grape-like crusts.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Agate is chalcedony with clear banding.
Side by side
| Property | Agate | Chalcedony |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6.5–7 | 6.5–7 |
| Luster | Waxy to vitreous | Waxy |
| Streak | White | White |
| Colors | Red, Orange, White, Gray, Brown, Blue | Blue, White, Gray |
| Crystal system | Microcrystalline quartz (chalcedony) | Microcrystalline quartz |
| Specific gravity | 2.58–2.64 | 2.58–2.64 |
| Formula | SiO₂ | SiO₂ |
| Found in | Lake Superior shores; Rio Grande do Sul, Brazil | Oregon; Namibia |
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 chalcedony
- Waxy, translucent and milky.
- Bubbly 'botryoidal' surfaces are common.
- No crystal faces; scratches glass.
Crystal system: Microcrystalline quartz
Full Chalcedony guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday