Rock IdentifierAgate & Jasper
Key takeaways
- Both are microcrystalline quartz (chalcedony), Mohs ~7.
- Agate is translucent and banded; jasper is opaque and solid-colored.
- Cheap dyed agate slices are common — vivid unnatural colors are the giveaway.
Same mineral, different look
Agate and jasper are both chalcedony — quartz built from crystals too small to see. The difference is transparency and pattern. Agate is translucent and famously banded, formed as silica-rich water deposited layer after layer in a cavity. Jasper is opaque, densely packed with impurities, and usually shows solid earthy colors or mottled patterns rather than clean bands.
How to recognize them
Both are hard (they scratch glass), waxy to glassy in luster, and break with conchoidal fracture. Hold a thin edge to light: agate lets some through and reveals curved bands; jasper stays opaque. Agates often start as nodules with a crystal-lined center (moving toward a geode); jasper tends to occur in solid masses and seams.
Dyeing & fakes
Because agate is porous between its bands, it takes dye readily — those neon-blue, magenta, and green agate slices sold cheaply are almost always dyed. Natural agate colors are usually more muted (white, grey, brown, soft blue). Suspiciously electric, perfectly even color, especially concentrated along the bands, signals dye rather than nature.
Value notes
Most agate and jasper are inexpensive and popular for tumbling and cabochons. Value climbs for distinctive patterns and named varieties — fortification agate, moss agate, ocean jasper, picture jasper — where the pattern tells a little story. Provenance and a striking, undamaged pattern matter more than sheer size.
