mineral

Polished agate/jasper slab

Microcrystalline quartz (chalcedony), primarily SiO₂, with iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; purple, red-brown, orange, and gray banding with a waxy to vitreous luster. It has cryptocrystalline quartz structure, no distinct cleavage, and typical specific gravity of about 2.6.

Identified August 24, 2026More mineral →

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Physical properties

Formation & geological history

This is likely a cut and polished silica-rich nodule, formed when groundwater deposited chalcedony and quartz in volcanic cavities, with iron oxides producing red-brown colors. Such agates and jasper formed mainly during Cenozoic to older volcanic episodes, depending on locality.

Uses & applications

Used for decorative slabs, bookends, cabochons, carvings, and lapidary collections; polished pieces have modest ornamental value.

Geological facts

The translucent purple-gray areas are characteristic of chalcedony or amethystine quartz, while opaque red-brown zones are jasper-like and iron stained.

Field identification & locations

Identify by hardness, curved or irregular color banding, translucency at thin edges, and resistance to scratching by a steel knife. Common sources include Brazil, Uruguay, Mexico, Madagascar, and the western United States.