gemstone

Black onyx or black agate bead necklace

Microcrystalline quartz, SiO₂ (likely chalcedony/black agate; possibly dyed)

AI-generated identification · may be incorrect

Polished, opaque to slightly translucent black beads with vitreous luster; quartz hardness ~6.5–7 Mohs, trigonal crystal structure, no cleavage, specific gravity ~2.6. The exceptionally uniform color suggests dyed chalcedony or black glass imitation, though the image alone cannot confirm.

Identified August 31, 2026More gemstone →

Explore Black onyx or black agate bead necklace in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Natural chalcedony forms when silica-rich groundwater fills cavities and fractures, commonly in volcanic rocks; deposits range from Paleozoic to recent. Black color may be natural, caused by inclusions, or artificially enhanced by dyeing.

Uses & applications

Used for beads, cabochons, carvings, and ornamental jewelry; common-quality strands typically have modest value.

Geological facts

“Black onyx” in the jewelry trade often refers to uniformly black chalcedony, frequently treated. Genuine stone beads feel cool, are harder than steel, and usually show subtle internal color variation.

Field identification & locations

Common sources include Brazil, Uruguay, India, Madagascar, and Mexico. Check with a loupe for banding or dye concentration in drill holes; glass may show bubbles and scratches more easily.