Rock Identifier
Banded Agate (Cryptocrystalline Quartz (SiO2)) — mineral
mineral

Banded Agate

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, and white concentric banding; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness
6
Color
Brown, tan, and white concentric banding
Luster
Waxy to vitreous
Identified More mineral

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, and white concentric banding; Luster: Waxy to vitreous; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Formation & geological history

Formed through the deposition of silica from groundwater into cavities (vesicles) in igneous rocks, specifically volcanic lavas. The banding represents pulse-like deposition cycles over thousands of years.

Uses & applications

Used primarily for jewelry (cabochons, beads), decorative carvings, and as pocket stones. Historically used for making mortar and pestles due to its hardness and resistance to chemicals.

Geological facts

The distinct bands are often thinner than a human hair. No two agates are identical, making them favorites for collectors. Agates have been used in amulets and jewelry since the time of Ancient Babylon.

Field identification & locations

Identify by its characteristic waxy luster and distinct parallel or concentric bands. It is frequently found in riverbeds, shorelines (like the Great Lakes), and volcanic regions. It will scratch glass but cannot be scratched by a steel knife.