mineral

Agate (Chert/Chalcedony)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Tan, white, orange-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness: 6
Color: Tan, white, orange-brown
Luster: Waxy to vitreous

Identified May 5, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Tan, white, orange-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Formation & geological history

Formed as a secondary mineral in volcanic or sedimentary rocks, often filling cavities (vesicles) or cracks via silica-rich groundwater. Frequently occurs in riverbeds or as glacial till deposits.

Uses & applications

Used in gemstone collecting, jewelry (cabochons), industrial abrasives, and historically for making tools (knapping).

Geological facts

The banding seen in the cross-section is characteristic of chalcedony. This specimen shows a thick weathered cortex (outer rind) hides the waxy silica interior.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture, waxy internal appearance, and its ability to scratch glass. Found globally in areas with volcanic history or ancient riverbeds.