mineral

Gray Agate

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Smoky gray with translucent layers; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Smoky gray with translucent layers
Luster: Waxy to vitreous

Identified May 31, 2026More mineral →

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Physical properties

Formation & geological history

Formation occurs primarily in volcanic rock cavities (vesicles) or gas bubbles where silica-rich groundwater deposits layers of microcrystalline quartz over thousands of years. Usually found in ancient lava flows.

Uses & applications

Commonly used for lapidary work, decorative beads, polished healing stones, tumbling, and as a low-cost gemstone for jewelry.

Geological facts

Agate is named after the Achates River in Sicily. It is known for its banding, though solid or subtly layered gray varieties are very common. It has been used for making ornaments for over 3,000 years.

Field identification & locations

Identify in the field by its waxy luster and conchoidal (shell-like) fracture. Look for it in riverbeds or near ancient volcanic outcrops. It is tough and resistant to weathering.