mineral

Black Onyx

Silicon Dioxide (SiO2) with parallel banding

Hardness: 6.5-7 (Mohs scale); Color: Solid black (often treated) or black with white bands; Luster: Vitreous to silky; Crystal structure: Hexagonal (trigonal); Cleavage: None; Specific Gravity: 2.65-2.67

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

Identified May 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a result of gas cavities in volcanic lava filling with silica-rich water. It is a variety of chalcedony quartz that grows over millions of years through layer-by-layer deposition.

Uses & applications

Primarily used in jewelry for rings, pendants, and carved cameos; also popular for decorative stone carvings and as a healing stone in metaphysical practices.

Geological facts

The word 'Onyx' comes from the Greek word for 'fingernail' or 'claw' because the white banding suggests a fingernail. Many solid black onyx stones are actually grey chalcedony that has been dyed for a uniform color.

Field identification & locations

Identify by its waxy-to-vitreous appearance and lack of visible crystalline grain. It is often confused with black agate or obsidian (which is glassier). Found commonly in Brazil, India, Madagascar, and the USA.

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mineral