Bands
Straight layers
Onyx names chalcedony whose layers run straight and roughly parallel; agate layers more often follow the wall of the cavity.
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Stone Explorer Onyx
Onyx, names and layers.
Separate banded onyx, sardonyx and commercial black chalcedony. Look at the layers, examine colour treatment and distinguish carbonate stone sold under the same name.
Two records
Two ways in · pick one
Each specimen opens its own file.
How to read the wall
One name, several materials.
A photograph can show layers and colour. It cannot establish whether a black colour is natural or applied, or which material carries the name.
Colour
Natural or applied
Natural and applied colour can occupy the same range. A photograph alone cannot tell them apart.
Name
Two stones, one word
Onyx marble is a banded carbonate stone, a different material from silica onyx.
Sources and image credits
Every claim keeps its scope.
The references below describe onyx as a material, its names and its treatments. The photographs describe two particular pieces. None of it certifies a BE. lot.
GIA, Wedding Anniversary Gemstones, Onyx sectionMaterial reference · scope of use
- Use
- Straight parallel chalcedony bands; dyeing of commercial black onyx.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
Götze, Möckel & Pan (2020), Mineralogy, Geochemistry and Genesis of AgateMaterial reference · scope of use
- Use
- Review of banded silica formation, mineralogy and open questions; not a universal onyx deposit model.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
GIA, August birthstones, Sardonyx sectionMaterial reference · scope of use
- Use
- Sard/onyx colour band nomenclature and treatment boundary.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
GIA, Identifying Black Opaque Gem Materials (1996)Material reference · scope of use
- Use
- Laboratory identification of black opaque materials; appearance alone insufficient.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
Estonian Museum of Natural History, ELM G229:203Material reference · scope of use
- Use
- Catalogued onyx, Australia; collection record, not treatment analysis.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
Oxford University Museum (2012): Alabaster and travertineMaterial reference · scope of use
- Use
- Onyx marble as a banded carbonate stone, separate from silica onyx.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
GIA: An Introduction to Gem TreatmentsMaterial reference · scope of use
- Use
- Dyeing of chalcedony in many colours.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
Hart (1927), The Nomenclature of SilicaMaterial reference · scope of use
- Use
- Historical use of onyx, sardonyx and nicolo as silica names.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
Gliozzo (2019), Variations on the silica theme, §5.5Material reference · scope of use
- Use
- Onyx, sardonyx and nicolo; natural and applied colour in banded silica.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
GIA, Gems & Gemology Winter 1986Material reference · scope of use
- Use
- Reports virtually all so-called black onyx as treated.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
CIBJO, The Gemstone Book (2022)Material reference · scope of use
- Use
- Lists trade Onyx (black) as dyed (always), and black-and-white straight-layered onyx as dyed (commonly).
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
GIA, Gems & Gemology Winter 1988Material reference · scope of use
- Use
- A strand of beads in which some black beads were surface-coated; the coating wore at the edges and came off with acetone.
- Limit
- This reference does not identify or certify a BE. specimen.
- Link
- Open source ↗
Specimen photographsImage credits · reference specimens
- Onyx · museum specimen
- Tõnis Saadre / Estonian Museum of Natural History · CC BY-SA 4.0. Resized; colour and original labels preserved.
- Onyx · Mainz Basin
- Mhrobben · CC BY-SA 4.0. Resized; colour preserved.
Formation illustrationExplanatory model · not site data
- Use
- Illustrates the bounded formation pathway described in this Explorer.
- Limit
- The drawing is not a measured field section, microscopy image or record of a BE. product.
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Questions about Stone Explorer
Which onyx records can I compare?
A catalogued onyx specimen from the Estonian Museum of Natural History and a banded onyx fragment from a sand pit in the Mainz Basin, Germany.
Can a photograph show whether onyx colour is natural?
No. Natural and applied colour can look the same in a photograph; a stone's treatment status comes from its documented record, not from its colour.
What does the onyx formation view show?
One cavity-filling example for banded silica, from an opening in the rock to a cut section through the layers.