Grey Chalcedony (Agate)

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: Translucent smoky grey to bluish-grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58–2.64

Formation & Geological History

Formed through the deposition of silica-rich groundwater in cavities of igneous and sedimentary rocks. It often forms at relatively low temperatures near the Earth's surface.

Uses & Applications

Commonly used in jewelry (cabochons, beads, carvings), ornamental objects, and historically for seals and cameos. Industrially used for mortar and pestles due to its hardness.

Geological Facts

Chalcedony is a cryptocrystalline form of quartz, meaning its crystals are too small to be seen even under a regular microscope. It has been used for making tools and jewelry since the Bronze Age.

Field Identification & Locations

Identify in the field by its waxy luster, conchoidal fracture (breaks like glass), and lack of visible crystal faces. Found worldwide in volcanic pockets, particularly in Brazil, India, and the USA.

Identified on: 4/18/2026

Mode: Standard