gemstone

Tumbled milky agate or chalcedony

Microcrystalline quartz, SiO₂ (chalcedony/agate variety)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent creamy-white body with brown iron-oxide staining, waxy to vitreous luster, cryptocrystalline structure, and no visible cleavage. Specific gravity is approximately 2.60–2.65.

Identified September 15, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities or fractures in volcanic rock, depositing microscopic quartz fibers and occasional iron oxides. Agates commonly formed in volcanic environments during the Cenozoic and older geological periods.

Uses & applications

Used as an inexpensive cabochon, bead, tumbled stone, ornament, and lapidary material; durable enough for jewelry and decorative objects.

Geological facts

The specimen appears polished and rounded, so its original banding may be subtle or absent; brown patches are likely limonite or hematite inclusions.

Field identification & locations

Identify by its glass-scratching hardness, waxy appearance, translucency, and lack of cleavage; common sources include Brazil, Uruguay, India, Madagascar, and the western United States. A hardness test should be performed only on an inconspicuous area.