mineral

Agate (translucent slice)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored bands, milky white to translucent grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.60 to 2.65

Hardness: 6
Color: Multi-colored bands, milky white to translucent grey
Luster: Waxy to vitreous

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed in cavities (vesicles) of volcanic rocks (basalt or andesite) or metamorphic rocks where silica-rich groundwater deposits layers of chalcedony over time. Specimens can range from millions to hundreds of millions of years old.

Uses & applications

Commonly used in jewelry (pendants, beads), ornamental carvings, burnishing tools, and historically for precision bearings and laboratory mortars due to its hardness and chemical resistance.

Geological facts

Agate belongs to the chalcedony family. Its name comes from the Achates River in Sicily where it was first discovered by ancient Greeks. No two agates are identical because the banding depends on the mineral inclusions in the groundwater during formation.

Field identification & locations

Identify in the field by its waxy luster, translucency when held to light, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds, beaches, and weathered volcanic areas like Lake Superior (USA), Brazil, and Germany.

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