mineral

Botryoidal chalcedony/geode fragment

Chalcedony, microcrystalline quartz (SiO₂), likely iron-oxide coated

AI-generated identification · may be incorrect

Dark gray-blue, waxy to dull luster with conchoidal fracture; hardness about 6.5–7 Mohs, no cleavage, trigonal quartz structure, specific gravity near 2.6. The orange-brown coating is likely limonite/goethite staining.

Identified September 19, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater filled cavities or vesicles in volcanic rock, depositing microcrystalline quartz in layers; iron-bearing fluids later produced the ochre coating. Such specimens are generally Cenozoic to older, depending on host rock.

Uses & applications

Used as ornamental stone, cabochons, carvings, and lapidary material; attractive coated pieces are collected as mineral specimens.

Geological facts

Chalcedony commonly forms botryoidal or massive crusts and may be blue-gray, gray, white, or banded. The apparent blue color can result from microscopic inclusions or light scattering rather than a distinct blue mineral.

Field identification & locations

Identify by its waxy appearance, curved conchoidal fracture, lack of cleavage, and hardness sufficient to scratch glass. Common worldwide, especially in volcanic regions; likely localities include Brazil, Uruguay, Mexico, India, and the western United States.