mineral

Agate (specifically, a slice of a Blue Lace or Chalcedony Agate nodule)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

Hardness: 6.5-7 (Mohs scale); Color: Pale blue, grey, and white with translucent banding; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Monoclinic (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: Pale blue, grey, and white with translucent banding
Luster: Waxy to vitreous

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary deposit in volcanic rock cavities (vesicles) or sedimentary fissures. Silica-rich groundwater percolates through cavities, depositing layers of chalcedony over thousands of years. Common in volcanic regions spanning from the Permian to Cenozoic eras.

Uses & applications

Commonly used in jewelry (cabochons, beads), decorative lapidary arts (coasters, bookends), and historically for precision mechanical parts like pivot bearings in scales due to its hardness and wear resistance.

Geological facts

Agates were used by the Ancient Greeks and Egyptians for amulets and seals. Every agate nodule is unique; no two pieces will ever have the exact same banding pattern. The banding is caused by rhythmic crystallization or variations in iron and manganese content during formation.

Field identification & locations

Identify in the field by looking for 'potato-like' nodules with a rough, pitted exterior (cortex) that feels significantly heavier than local limestone. To verify, look for conchoidal (shell-like) fractures where it has chipped. Common locations include Brazil, Uruguay, Namibia, and the Great Lakes region of the USA.

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