mineral

Chalcedony Geode Fragment

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, orange-brown, translucent to opaque; Luster: Waxy to vitreous; Crystal structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.58-2.64.

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

Identified June 30, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in volcanic environments through the precipitation of silica-rich groundwater in cavities (vesicles) of basalt or rhyolite. Can also form in sedimentary rocks like limestone.

Uses & applications

Used for decorative items, jewelry (cabochons), talismans, and as an ornamental stone in lapidary arts. Small fragments are common desktop curios or pocket stones.

Geological facts

Chalcedony is composed of microscopic crystals of quartz and moganite. The term 'geode' refers to the hollow or semi-hollow cavity where crystals grew toward the center from the outer shell.

Field identification & locations

Identify in the field by its waxy luster, hardness (it will scratch glass), and lack of cleavage. Often found in dry washes, riverbeds, or volcanic ash beds. This specimen shows a druzy or botryoidal interior surface.

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