mineral

Tumbled jasper and agate specimens

Microcrystalline quartz (chalcedony), chiefly SiO₂, with iron-oxide and other mineral impurities

AI-generated identification · may be incorrect

Opaque to translucent polished chips with mustard-yellow, brown, red-purple, and gray colors; waxy to vitreous luster; hardness about 6.5–7 Mohs; no cleavage; cryptocrystalline structure. The banded gray-yellow piece may be jasper or agate, while the purple piece could be amethyst-bearing chalcedony.

Identified August 23, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing chalcedony, quartz, and colored impurities over long periods, commonly from the Cenozoic to older volcanic ages. Exact locality cannot be determined from the image.

Uses & applications

Used for cabochons, beads, carvings, tumbled stones, ornaments, and decorative inlay; durable varieties are also used as lapidary material.

Geological facts

Color zoning commonly reflects iron oxides, manganese, clay, or other inclusions; purple coloration indicates trace iron exposed to natural irradiation. Polishing enhances its waxy surface and patterns.

Field identification & locations

Identify by testing for quartz-like hardness, lack of cleavage, waxy luster, and conchoidal fracture; glass should not scratch it. Common sources include Brazil, India, Madagascar, Uruguay, Mexico, and the western United States.