Grey Agate

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Grey, black, white, sometimes banded. Luster: Waxy to vitreous. Crystal system: Trigonal (cryptocrystalline). Cleavage: None. Specific Gravity: 2.60-2.65.

Formation & Geological History

Formed in volcanic and metamorphic environments as silica-rich water fills cavities (geodes) or cracks in rocks. Layering occurs over thousands of years as thin layers of minerals crystallize.

Uses & Applications

Used primarily in jewelry making (beads, cabochons), ornamental decoration, and as industrial mortar and pestles due to its hardness and resistance to chemicals.

Geological Facts

Grey agate is often called 'The Stabilizer.' While common, high-quality specimens showing distinct concentric banding or druzy (crystal) pockets are highly sought after by collectors.

Field Identification & Locations

Identify in the field by its conchoidal fracture (smooth, curved breaks) and its inability to be scratched by a steel knife. It is frequently found in riverbeds or near volcanic basalt outcrops.

Identified on: 5/7/2026

Mode: Standard