mineral

Grey Agate (Banded Chalcedony)

Agate (Silicon Dioxide - SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Gray, white, or blue-grey with concentric banding; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Gray, white, or blue-grey with concentric banding
Luster: Waxy to vitreous

Identified March 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic and metamorphic rocks. Agates develop through the deposition of silica from groundwater in the cavities of igneous rocks, building up in layers over thousands of years. They are found in many geological ages ranging from the Archaean to the Cenozoic.

Uses & applications

Commonly used in lapidary for jewelry (beads, cabochons), ornamental carvings, and historical use in making precision tools like mortar and pestles due to its high hardness and chemical resistance.

Geological facts

Agate was first named by Theophrastus, a Greek philosopher, who discovered the stone along the shore line of the Dirillo River in Sicily. It is one of the oldest minerals in recorded history and was once valued as a protection amulet.

Field identification & locations

Identify in the field by its translucent appearance when held to light and its characteristic waxy luster. It is common in riverbeds and volcanic regions in Brazil, India, and the United States (Lake Superior). Collectors should look for clean, distinct banding.

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