mineral

Weathered agate/chalcedony nodule

Microcrystalline quartz (SiO₂), likely agate with iron-oxide staining

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; cream, tan, rusty brown, and gray colors with waxy to dull luster. Cryptocrystalline quartz lacks visible individual crystals; the rounded patches may represent banded or botryoidal chalcedony, though the surface is heavily weathered.

Identified August 29, 2026More mineral →

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Physical properties

Formation & geological history

Agate forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in layers; iron oxides create the brown-red staining. The specimen’s precise geological age and locality cannot be determined from the photograph.

Uses & applications

Used as a lapidary material for cabochons, slabs, beads, carvings, and polished specimens; decorative agate is also used for bookends and ornaments.

Geological facts

Agate commonly reveals concentric banding when cut and polished, but weathering can obscure its pattern and produce a porous-looking rind.

Field identification & locations

Identify by its very hard, glass-scratching surface, waxy texture, curved/concentric chalcedony patterns, and lack of obvious cleavage. Common in volcanic terrains and gravel deposits worldwide; avoid assuming the brown areas are copper minerals without testing.