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Variety · Silicate

Onyx

SiO₂

Parallel-banded black-and-white agate; most black 'onyx' is dyed chalcedony.

Hardness7
Crystal systemTrigonal
ClassSilicate
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Onyx specimen

Black oval onyx cabochons — Photo: W.carter · CC BY 4.0

Onyx

Also known as: Black onyx.

The straight-banded black-and-white variety of agate — carved since antiquity; sardonyx adds red bands.

Intro adapted from Wikipedia (CC BY-SA).

Onyx is a mineral variety of Quartz, with the chemical formula SiO₂.

It crystallizes in the trigonal crystal system.

Key properties: Mohs hardness 7; typically black or white.

Collections: Gemstones.

Index entry. This entry combines official IMA/RRUFF species data with published physical-property data and a Wikipedia introduction — a full written entry hasn’t been published yet. Browse more O minerals or help write this entry.