Gemstone profile and identification guide
Onyx
Onyx is a parallel-banded chalcedony variety of quartz, traditionally black and white in layered form.
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Overview
Onyx is a parallel-banded chalcedony variety of quartz, traditionally black and white in layered form.
Did you know? Historic cameo carving often used layered onyx and sardonyx for contrast.
Use this profile as a collector reference and educational guide for quick on-page comparison, then validate with the interactive identification system.
Identification
Name: Onyx
Scientific classification: Silicate (Chalcedony Quartz)
Hardness: 7 Mohs
Transparency: translucent
Lustre: waxy
Crystal system: Trigonal (microcrystalline aggregate)
Primary colour: Black
Secondary colour: White
Colour family: Blacks
Look for chalcedony texture with parallel banding, quartz hardness, and waxy lustre.
Verification Status
Status: verified-core-fields
Reference priority: GIA, Gem-A, Mindat, International Gem Society
Core identity, locality, and physical-property fields reviewed against standard gemological references.
Values are given as practical gemological ranges where appropriate.
Physical Properties
Hardness category: hard
Hardness value: 7 Mohs
Chemical composition: Silicon dioxide (SiO2)
Crystal system: Trigonal (microcrystalline aggregate)
Common locations: Brazil, Uruguay, India, Mexico, Pakistan
Learn more: Gem-A gemstone education resources.
Colour Variations
Banded black and white chalcedony; all-black trade material is often treated.
Optical effects: Banded Structure
Detailed Gemology
Mineral species: Quartz (chalcedony onyx variety)
Mineral group: Quartz group
Chemical formula: Silicon dioxide (SiO2)
Mohs hardness: 7
Crystal system: Trigonal (microcrystalline aggregate)
Lustre: waxy
Transparency: translucent
Streak: White
Cleavage: None
Fracture: Conchoidal
Specific gravity: 2.58-2.64
Refractive index: 1.53-1.54
Optical phenomena: Banded structure
Colour range: Black and white banded; brown-white in sardonyx-related material
Common inclusions: Band boundaries, fractures, iron/manganese staining
Geological environment: Silica deposition in volcanic and sedimentary cavities
Principal mining regions: Brazil, Uruguay, India, Mexico, Pakistan
Important commercial sources: Most commercial onyx in jewellery is produced from chalcedony rough from Brazil and Uruguay, often with treatment
Historical significance: Important historical material for seals, cameos, and intaglios.
Common treatments: Black dyeing and sugar-acid treatment are common.
Synthetic or imitation forms: Dyed chalcedony and glass are common imitations.
Common look-alikes: Black agate, dyed chalcedony, obsidian
Jewellery uses: Used in cabochons, intaglios, beads, and architectural inlay.
Care recommendations: Generally durable at Mohs 7; avoid harsh chemicals for dyed or impregnated material.
Cross-check profile data with GIA Gem Encyclopedia and Mindat entry for Onyx.
Formation
Forms from successive silica deposition in cavities, creating parallel chalcedony bands.
Origin
Most commercial onyx in jewellery is produced from chalcedony rough from Brazil and Uruguay, often with treatment
Uses
Best for: Used in cabochons, intaglios, beads, and architectural inlay.
Ideal uses: High-contrast carvings, signet styles, and banded cabochons.
Care
Generally durable at Mohs 7; avoid harsh chemicals for dyed or impregnated material.
Need another candidate? Use advanced gemstone search or return to the identification guide.
Related gemstones by colour
Related gemstones by hardness
Gemstones from the same mineral family
Commonly confused gemstones
Onyx FAQ
How can I identify Onyx?
Compare hardness (7 Mohs), crystal system (Trigonal (microcrystalline aggregate)), colour profile, and lustre (waxy) with your sample. Then cross-check related gemstones listed above.
What colour range does Onyx appear in?
Banded black and white chalcedony; all-black trade material is often treated.
Where is Onyx commonly used?
High-contrast carvings, signet styles, and banded cabochons.. For maintenance, follow the care guidance in this profile.
Scientific References
GIA: general gemstone identity (reviewed) - Batch 01 factual verification pass.
Gem-A: gemological terminology and testing references (reviewed) - Batch 01 factual verification pass.
Mindat: mineral species and principal localities (reviewed) - Batch 01 factual verification pass.
International Gem Society: gem trade context and treatment overview (reviewed) - Batch 01 factual verification pass.