gemstone

Polished agate bead bracelet

Agate, a banded microcrystalline variety of quartz (SiO₂), likely mixed-color dyed or naturally colored chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; waxy to vitreous luster; translucent to opaque; cryptocrystalline quartz with no visible cleavage; specific gravity about 2.60–2.65. The beads show yellow, brown, green, gray, and reddish colors, possibly enhanced by dye or heat treatment.

Identified August 31, 2026More gemstone →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony and quartz in layers over long periods, commonly during the Cenozoic or older volcanic episodes. Individual beads are cut, drilled, polished, and possibly treated by humans.

Uses & applications

Used for inexpensive jewelry, ornamental objects, carvings, and lapidary collections. Typical value is about $10–$40 for a bracelet; unusually fine natural agate may command more.

Geological facts

Agate’s microscopic banding reflects changing chemistry and silica deposition during cavity filling. Colorful green and yellow beads are often commercially dyed, especially when the colors are unusually uniform or vivid.

Field identification & locations

Identify by its glassy/waxy polish, hardness, cool feel, translucency, and occasional curved or banded patterns; it should resist scratching by a steel knife. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.