mineral

Agate

Silicon Dioxide (SiO2) - Chalcedony variant

Hardness: 6.5–7 on the Mohs scale. Color: Multicolored, often banded in grays, whites, and browns. Luster: Waxy to vitreous. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None. Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Multicolored, often banded in grays, whites, and browns
Luster: Waxy to vitreous

Identified March 9, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily within volcanic and metamorphic rocks. It occurs when silica-rich groundwater fills cavities (gas bubbles) in cooling lava or igneous rock, depositing layers of microcrystalline quartz over thousands of years.

Uses & applications

Extensively used in jewelry (cabochons, beads, pendants), ornamental carvings, and historical tool-making. In industry, it is used for precision pendulums, mortar and pestles, and burnishing tools due to its hardness.

Geological facts

Agate is named after the Achates River (now Dirillo River) in Sicily, where it was first discovered by Greek philosopher Theophrastus. It is a 'cryptocrystalline' variety of quartz, meaning its crystals are too small to be seen without a microscope.

Field identification & locations

Identify in the field by its characteristic waxy luster, translucency, and often visible concentric banding. Commonly found in Brazil, Uruguay, and the Lake Superior region of the USA. For collectors, look for intact banding and vibrant contrasts.