Agate Nodule (partially vuggy Quartz)

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: White, gray, and brown; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture).

Formation & Geological History

Formed as secondary deposits of silica in cavities of volcanic rocks or sedimentary formations. Silica-rich fluids percolate through voids over millions of years, often leaving a hollow 'vug' or pocket of crystals.

Uses & Applications

Used primarily for lapidary work, jewelry (cabochons), as collector decorative pieces, and historically for mortars and pestles due to its hardness.

Geological Facts

Agate is a variety of chalcedony. This specific specimen shows a 'vuggy' center where macrocrystalline quartz has grown into an open pocket, which is common in geodes and thunder eggs.

Field Identification & Locations

Identify by its hardness (scratches glass), waxy luster on broken surfaces, and specific gravity. Look for it in riverbeds, volcanic ash beds, or desert environments. This specimen is a small rough nodule.

Identified on: 4/15/2026

Mode: Standard