mineral

Chalcedony (Agate/Quartz pebble)

Silicon dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5-7 on Mohs scale. Color: Translucent white to milky grey with waxy luster. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Lacks visible cleavage and has a conchoidal fracture. Specific gravity: 2.6-2.64.

Hardness: 6
Color: Translucent white to milky grey with waxy luster

Identified January 24, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich groundwater into cavities in volcanic rocks or within sedimentary layers. It can form at low temperatures over millions of years, often as a secondary mineral.

Uses & applications

Commonly used in jewelry as gemstones (when polished), lapidary art, and historically for tools due to its sharp conchoidal fracture. In industry, high-purity quartz is used in glassmaking and electronics.

Geological facts

Chalcedony is a broad term that includes agate, jasper, and onyx. It was one of the earliest minerals used by humans to create sharp scrapers and arrowheads. Unlike macrocrystalline quartz (like amethyst), its crystals are too small to see even under a light microscope.

Field identification & locations

Identify in the field by its waxy appearance, translucency (hold it up to a light), and smooth, rounded surface if found in riverbeds. It will easily scratch glass but cannot be scratched by a steel knife. Commonly found in gravel pits, dry washes, and volcanic regions.

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Mineral/Rock

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