What's That Rock?Onyx
Chalcedony with straight, parallel black and white bands. Most black onyx on the market is dyed.
How to identify Onyx
- Straight parallel bands, unlike the curved bands of agate
- Hard: scratches glass
- Smooth, waxy polished surface
Often confused with
- Agatecurved bands
- Banded calcite sold as 'onyx marble' or 'Mexican onyx'soft, fizzes in acid
- Black glass
Real or fake?
- Plain, jet-black onyx is usually dyed; this is traditional and common
- Soft 'onyx' that fizzes in acid is calcite, not onyx
Is Onyx valuable?
Inexpensive.
Typical retail prices
Tumbled stone$1–4each
Cut gemstone$1–5per carat
Typical retail ranges in US dollars, compiled from public dealer and marketplace listings in October 2026. Real prices vary widely with quality, size and origin. This is general information, not an appraisal.
What changes the price
- Natural or dyed: plain black onyx is usually dyed, and that is traditional
- 'Mexican onyx' is banded calcite, much softer and cheaper than true onyx
- Banding: true sardonyx with crisp black-and-white banding costs more
- Cut: large flat slabs and carvings cost more than tumbled pieces
Uses
- Beads, cameos, carvings
Care
Safe to wash.
Identifying a stone from a description or a photo is an estimate. Many stones look alike. Ask an expert or a gem lab before you buy, sell or rely on an identification.
Updated October 2026