mineral

Polished agate with druzy quartz

Microcrystalline chalcedony (SiO₂) with crystalline quartz and iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, brown, and rust-red colors; waxy to vitreous luster; cryptocrystalline chalcedony matrix with visible quartz crystals and no prominent cleavage. The rounded, polished surface indicates a tumbled or cut specimen.

Identified August 19, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and later quartz in layers or crystal-lined voids. Iron oxides create the brown-red coloration; formation commonly occurred during relatively young volcanic episodes, though exact age depends on locality.

Uses & applications

Used for cabochons, ornaments, beads, décor, and lapidary collections; attractive druzy pieces may be set in jewelry.

Geological facts

Agate is a variety of chalcedony, and its banding or cavity fillings record successive pulses of silica deposition. “Druzy” describes the coating of tiny quartz crystals visible in open cavities.

Field identification & locations

Identify by its translucent chalcedony, irregular internal pattern, quartz sparkle, and hardness sufficient to scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.