mineral

Banded Black Onyx (Chalcedony)

Silicon Dioxide (SiO₂)

Hardness: 6.5–7 (Mohs scale); Color: Black with white parallel bands; Luster: Vitreous to silky; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.65–2.66

Hardness: 6
Color: Black with white parallel bands
Luster: Vitreous to silky

Identified March 7, 2026More mineral →

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Physical properties

Hardness: 6.5–7 (Mohs scale); Color: Black with white parallel bands; Luster: Vitreous to silky; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.65–2.66

Formation & geological history

Formed as a cryptocrystalline variety of quartz when silica-rich thermal fluids deposit layers in gas cavities (vesicles) within volcanic rocks or sedimentary environments. Most commercial deposits originate from the Mesozoic or Cenozoic eras.

Uses & applications

Predominantly used for ornamental carvings, jewelry (cabochons and beads), intaglios, cameos, and metaphysical decorative items.

Geological facts

In Greek, 'Onyx' means 'fingernail' or 'claw,' referring to a myth where Cupid cut Venus's fingernails and they turned into stone. Historically, it was highly prized by the Romans for seal rings because the wax would not stick to the stone.

Field identification & locations

Identify by looking for perfectly parallel, straight bands (unlike the concentric curved bands of many agates). To distinguish from synthetic glass, check for coldness to the touch and a lack of air bubbles. Common locations include Brazil, Uruguay, India, and Madagascar.

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