mineral

Black Onyx

Silicon Dioxide (SiO2) with parallel banding

Hardness: 6.5-7 on Mohs scale; Color: Solid black (often treated) or black with white bands; Luster: Vitreous to silky; Crystal Structure: Trigonal (cryptocrystalline); Specific Gravity: 2.65-2.67

Hardness: 6
Color: Solid black (often treated) or black with white bands
Luster: Vitreous to silky

Identified June 2, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Solid black (often treated) or black with white bands; Luster: Vitreous to silky; Crystal Structure: Trigonal (cryptocrystalline); Specific Gravity: 2.65-2.67

Formation & geological history

Formed in the gas cavities (vughs) of volcanic lava; mineral-rich water precipitates silica layers over time. Typical of metamorphic or igneous environments where silica-rich fluids permeate rock.

Uses & applications

Used extensively in jewelry for rings and beads, ornamental carvings, intaglios, and historically used for stone seals and amulets.

Geological facts

Legend says that Cupid clipped Venus's fingernails and the clippings fell to Earth, turning into Onyx. While natural black onyx exists, most commercial solid black onyx is dyed chalcedony.

Field identification & locations

Identified by its high hardness (won't be scratched by a knife) and smooth, waxy luster. Found globally, prominent sources include Brazil, India, Madagascar, and the USA.

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