mineral

Botryoidal chalcedony (likely blue-gray agate)

Chalcedony, microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; blue-gray to pale gray, waxy to vitreous luster, massive/botryoidal texture, no obvious cleavage, and specific gravity near 2.6. The rounded, crust-like surface and translucent edges are characteristic of chalcedony.

Identified August 28, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, commonly growing as concentric or botryoidal coatings. It may range from Cenozoic to much older depending on its host rock.

Uses & applications

Used for cabochons, carvings, beads, and small decorative specimens; larger varieties are used as agate ornaments and lapidary material. This small rough piece has modest commercial value.

Geological facts

Blue-gray coloration can result from microscopic inclusions or trace minerals; the specimen may also be a drusy chalcedony fragment with tiny quartz crystals. Identification is best confirmed by a scratch test and examination of translucency.

Field identification & locations

Common in volcanic regions worldwide, including Brazil, Uruguay, Mexico, the western United States, and India. Look for hardness greater than glass, a waxy surface, curved fracture, and absence of visible cleavage.