mineral

Polished agate (likely seam or plume agate)

Microcrystalline quartz, SiO₂, chiefly chalcedony with possible quartz and iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, tan, brown, and cream banding with a waxy to vitreous luster. Trigonal quartz occurs as cryptocrystalline fibers; typically no visible cleavage, conchoidal fracture, and specific gravity near 2.6.

Identified August 26, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities in volcanic rocks, depositing chalcedony in successive layers; associated volcanic host rocks are commonly Cenozoic to Paleozoic, depending on locality.

Uses & applications

Used for cabochons, carvings, beads, bookends, and decorative polished specimens; durable enough for ornamental and limited industrial applications.

Geological facts

Its concentric or irregular bands develop from changing fluid chemistry, pressure, and silica saturation. The pictured rough underside appears to retain dark volcanic matrix.

Field identification & locations

Identify by translucency, curved banding, waxy luster, and conchoidal fracture; it commonly occurs in basaltic lava cavities worldwide, notably Brazil, Uruguay, Mexico, India, and the United States. Dyeing is common, but these muted natural colors appear plausible.