mineral

Banded Agate (Chert/Chalcedony)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Waxy grey with tan banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); SG: 2.58-2.64.

Hardness: 6
Color: Waxy grey with tan banding
Luster: Vitreous to waxy

Identified May 24, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Waxy grey with tan banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); SG: 2.58-2.64.

Formation & geological history

Formed through the deposition of silica from groundwater into cavities (vesicles) within igneous rocks or as nodules in sedimentary layers. These specific pieces show concentric banding characteristic of agate.

Uses & applications

Used primarily for jewelry (cabochons), lapidary art, collecting, and historically for making sharp stone tools due to its conchoidal fracture.

Geological facts

Agate is a variety of chalcedony. The banding is caused by the rhythmic crystallization of silica. It is often found within geodes or as weathered nodules in riverbeds.

Field identification & locations

Identify in the field by its waxy luster, smooth 'shell-like' curved fractures, and translucent edges. Look for it in areas with volcanic history or gravel beds.

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