Agate
Agate is a banded variety of chalcedony formed in concentric layers in volcanic rocks. Each layer represents a different period of mineral deposition.
Agate properties at a glance
| Type | Quartz Family |
|---|---|
| Chemical formula | SiO2 |
| Mohs hardness | 7 |
| Crystal system | hexagonal |
| Luster | waxy |
| Streak | White |
| Cleavage | None |
| Fracture | Conchoidal |
| Specific gravity | 2.6 |
| Transparency | translucent |
| Common colors | Banded, Blue, Brown, Red, Green, Gray |
| Rarity | common |
Geology & background
Forms in cavities of volcanic rocks when silica-rich water deposits layers of chalcedony over time.
Used for tools in the Stone Age and for ornamental objects since ancient Babylon.
How to identify Agate
- Check whether the specimen's color and texture match typical Agate examples.
- Photograph a fresh surface in natural light and avoid shadows, glare, or wet surfaces.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Where Agate is found
Agate is reported from multiple localities or geological settings. Exact locality should be verified from specimen provenance, maps, or field notes.
How much is Agate worth?
| Entry-level specimen | $5 |
|---|---|
| Typical collector specimen | $25 |
| Premium specimen | $300+ |
Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
Common uses
- Jewelry
- Decorative objects
- Bookends
- Coasters
Interesting facts
- Named after the Achates River in Sicily
- Some agates have been forming for millions of years
- Dyed agates have been made since Roman times
Care & safety
Treat Agate as a collector specimen unless hardness, cleavage, and fracture are confirmed.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a properly rated respirator.
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