mineral

Agate and Chalcedony Assortment

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored, translucent to semi-transparent; Luster: Vitreous to waxy; Crystal Structure: Trigonal (Microcrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.60-2.65.

Hardness: 6
Color: Multi-colored, translucent to semi-transparent
Luster: Vitreous to waxy

Identified June 26, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic and metamorphic rocks as silica-rich groundwater fills cavities (vesicles). They are cryptocrystalline varieties of quartz, often found in Cenozoic era volcanic deposits.

Uses & applications

Used extensively in jewelry as gemstones (cabochons and beads), ornamental carvings, burnishing tools, and for lapidary precision instruments due to their hardness.

Geological facts

Agates are famous for their distinct banding patterns, caused by rhythmic crystallization of silica layers. The Greek philosopher Theophrastus named the stone after the Achates River in Sicily where it was first discovered.

Field identification & locations

Identify in the field by looking for a waxy luster on fractured surfaces and a lack of visible crystal grains. These tumbled specimens are common in riverbeds and beaches in volcanic regions globally, such as Brazil, India, and the United States (Oregon/Lake Superior).