mineral

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Grayish-blue, milky white, tan crust; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Grayish-blue, milky white, tan crust
Luster: Waxy to vitreous

Identified July 13, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in volcanic rock cavities or sedimentary environments. This specimen shows a botryoidal (grape-like) texture in the vug and a weathered host-rock crust.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), and as a collector's specimen. Historically used for making stone tools due to its conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a normal microscope. It forms the basis for many gemstones including agate, jasper, and carnelian.

Field identification & locations

Identify by its waxy luster, hardness (it will scratch glass), and its lack of visible crystal faces despite being translucent. Found globally in volcanic regions and sedimentary beds.

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