mineral
Red-and-brown agate bead bracelet
Agate, a microcrystalline variety of quartz (SiO₂), likely colored chalcedony/carnelian
AI-generated identification · may be incorrectMohs hardness 6.5–7; rounded polished beads with waxy to vitreous luster, translucent to opaque red, orange, brown, and dark gray colors. Quartz has trigonal crystal structure but occurs here as fibrous cryptocrystalline chalcedony; no visible cleavage, conchoidal fracture, specific gravity about 2.60.
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Physical properties
Mohs hardness 6.5–7; rounded polished beads with waxy to vitreous luster, translucent to opaque red, orange, brown, and dark gray colors. Quartz has trigonal crystal structure but occurs here as fibrous cryptocrystalline chalcedony; no visible cleavage, conchoidal fracture, specific gravity about 2.60.
Formation & geological history
Agate forms when silica-rich groundwater fills cavities in volcanic rock, commonly producing concentric bands; colors derive from iron oxides and other impurities. The beads are human-cut and polished, and may be heat-treated or dyed; the geological age depends on the source deposit.
Uses & applications
Used for jewelry, beads, carvings, and ornamental objects; common polished agate has modest commercial value.
Geological facts
Agate is a variety of chalcedony rather than a separate mineral species. The varied red-brown material may also include carnelian and jasper-like opaque zones.
Field identification & locations
Identify by its quartz-like hardness, smooth polish, waxy luster, and subtle translucence; glass or plastic imitations are lighter and scratch more easily. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.
