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Onyx identification and geology

Onyx mineral reference specimen

Banded variety of chalcedony with parallel bands of black and white. Used since antiquity for cameos and intaglios. Color: Black and white banded. Luster: Waxy to vitreous. Streak: White. Cleavage: None. Hardness: 6.5-7. Transparency: Translucent to opaque. Crystal system: Hexagonal Trigonal. Chemical formula: SiO₂. Specific gravity: 2.60. Formation: Forms from layered deposition of silica in cavities, similar to agate but with straight parallel bands. Common geological settings: Brazil, India, Uruguay, USA; found in volcanic rocks. Common look-alikes and related entries: Agate, Obsidian, Jet.

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Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T14:37:37.418493+00:00
Review status
Published; not independently peer-reviewed
  • IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
  • Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.

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Common questions

What is Onyx?
Banded variety of chalcedony with parallel bands of black and white. Used since antiquity for cameos and intaglios.
How can you identify Onyx?
Compare several properties rather than relying on colour alone. This entry records colour: Black and white banded; lustre: Waxy to vitreous; streak: White; Mohs hardness: 6.5-7; cleavage: None; crystal system: Hexagonal Trigonal; transparency: Translucent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.
How does Onyx form?
Forms from layered deposition of silica in cavities, similar to agate but with straight parallel bands.
Where is Onyx commonly found?
Brazil, India, Uruguay, USA; found in volcanic rocks.
What is Onyx commonly confused with?
Onyx may be confused with Agate, Obsidian, Jet. Compare multiple diagnostic properties because colour and surface appearance can overlap.

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