sedimentary

Agate

Chalcedony (SiO2) with impurities

Hardness: 6.5-7. Color: Translucent grey-blue with brown/orange iron staining. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.58-2.64.

Hardness: 6
Color: Translucent grey-blue with brown/orange iron staining
Luster: Waxy to vitreous

Identified July 15, 2026More sedimentary →

Explore Agate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed as a secondary mineral in volcanic or metamorphic rock cavities, typically when silica-rich groundwater fills gas bubbles (vesicles) or cracks. Frequently found as 'river rocks' after erosion.

Uses & applications

Used for making jewelry, lapidary art, decorative carvings, and industrially for mortars and pestles or burnishing tools due to its hardness.

Geological facts

Agate is a variety of chalcedony characterized by its microcrystalline structure. The brown spotting seen here is likely iron oxide or limonite staining within the silica matrix.

Field identification & locations

Identify in the field by its translucency (when held to light), waxy feel, and conchoidal (glass-like) fracture patterns. Often found in riverbeds, gravel pits, and volcanic regions.