mineral
Chalcedony (likely brown agate or flint)
Microcrystalline quartz, SiO₂; chalcedony, possibly iron-stained
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent gray-brown with a waxy to glassy luster and irregular, conchoidal fracture. The small rough piece shows no obvious crystal faces; its exact variety cannot be confirmed from the image.
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Physical properties
Hardness 6.5–7 Mohs; translucent gray-brown with a waxy to glassy luster and irregular, conchoidal fracture. The small rough piece shows no obvious crystal faces; its exact variety cannot be confirmed from the image.
Formation & geological history
Silica-rich fluids precipitate microcrystalline quartz in cavities or fractures; iron impurities can produce brown hues. Chalcedony forms in many settings and spans a wide range of geological ages.
Uses & applications
Used for beads, carvings, cabochons, and decorative objects; flint varieties were historically important for tools and fire-starting.
Geological facts
Chalcedony is composed of quartz crystals too small to distinguish individually without magnification.
Field identification & locations
Look for a waxy surface, translucency at thin edges, and curved, shell-like fracture; it commonly occurs in volcanic rocks and sedimentary deposits. Image alone cannot distinguish chalcedony from flint or another silica-rich stone.
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