mineral

Tumbled gray agate (chalcedony)

Microcrystalline quartz, SiO₂; likely banded or translucent chalcedony

AI-generated identification · may be incorrect

Mohs hardness 6.5–7; gray to smoky, translucent, with a waxy-to-glassy luster and cryptocrystalline structure. The polished stones show no obvious cleavage; specific gravity is about 2.6.

Identified October 3, 2026More mineral →

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Physical properties

Mohs hardness 6.5–7; gray to smoky, translucent, with a waxy-to-glassy luster and cryptocrystalline structure. The polished stones show no obvious cleavage; specific gravity is about 2.6.

Formation & geological history

Agate forms as silica-rich fluids fill cavities in volcanic rocks, depositing chalcedony in layers. Its age varies by deposit, commonly millions to hundreds of millions of years.

Uses & applications

Tumbled agate is used in jewelry, beads, ornaments, and mineral collections; agate also has limited industrial use as a durable silica material.

Geological facts

Agate’s microscopic quartz fibers can produce fine bands, though no distinct banding is visible in these small polished pieces.

Field identification & locations

Common sources include Brazil, Uruguay, India, and the United States. Identify agate by its hardness, waxy sheen, translucence, and—when present—concentric bands; these pieces appear to be polished gray chalcedony.