mineral

Blue-gray chalcedony (likely blue agate)

Microcrystalline quartz, SiO₂

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, blue-gray to white mottling, waxy to dull luster, and no visible cleavage; cryptocrystalline quartz has a compact fibrous structure. The piece appears naturally worn or roughly shaped, though identification is limited by the photograph.

Identified September 13, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures, commonly in volcanic rocks; deposition may occur over long periods, generally from the Cenozoic to older volcanic episodes. Common sources include Brazil, Uruguay, Mexico, India, and the western United States.

Uses & applications

Used for cabochons, beads, carvings, tumbled stones, and decorative objects; massive low-grade material is inexpensive and occasionally used ornamentally.

Geological facts

Blue coloration can result from fine mineral inclusions, microscopic fibers, or irradiation-related effects; many intensely blue commercial specimens are dyed. Natural blue chalcedony is generally paler and more translucent.

Field identification & locations

Look for a smooth waxy surface, conchoidal fracture, translucency at thin edges, and hardness sufficient to scratch glass; it should not show calcite-like cleavage or fizz in weak acid. Confirm with a hardness, refractive-index, or laboratory test.