mineral

Agate

Silicon Dioxide / Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs). Color: Translucent brown, tan, and orange (carnelian tones). Luster: Waxy to vitreous. Crystal structure: Hexagonal (trigonal) cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Translucent brown, tan, and orange (carnelian tones)
Luster: Waxy to vitreous

Identified March 12, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in volcanic pockets (amygdules) or sedimentary cavities. Groundwater rich in silica slowly deposits layers of microcrystalline quartz over thousands of years. This specific specimen shows alluvial wear, suggesting it was transport by water.

Uses & applications

Used widely in lapidary arts for jewelry, cabochons, and decorative carvings. Historically used for mortar and pestles due to hardness, and used today as burnishing tools or in industrial precision bearings.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. It is famous for its 'banding' effect, though some nodules (like this one) may appear more uniform or mossy until sliced open.

Field identification & locations

Identify by its translucent quality when held to light and its smooth, waxy feel. Look for conchoidal (shell-like) fractures on broken edges. Commonly found in gravel beds, lake shores (like Lake Superior), and volcanic regions like Oregon, Brazil, and Germany.

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