Mineral

Black Agate (Banded)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Black with tan/white banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (Cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Black with tan/white banding
Luster: Vitreous to waxy

Identified June 20, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Black with tan/white banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (Cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & geological history

Formed in volcanic lava cavities (vesicles) or metamorphic rocks where silica-rich groundwater deposits layers over thousands of years. Common in Tertiary and Cretaceous volcanic formations.

Uses & applications

Used primarily in lapidary arts for jewelry, decorative carvings, and as a collector's gemstone. Also used in precision instruments like mortar and pestles due to hardness.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. The 'eye' or curved banding is the result of repetitive rhythmic crystallization during formation.

Field identification & locations

Identify by its characteristic banding, conchoidal fracture (curved glass-like breaks), and hardness. Often found in riverbeds or near ancient volcanic sites in Brazil, India, and the USA.