mineral

Chalcedony Pebble

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: brownish-grey with slight translucency; Luster: waxy to vitreous; Crystal structure: trigonal (microcrystalline); Cleavage: none, conchoidal fracture

Hardness: 6
Color: brownish-grey with slight translucency
Luster: waxy to vitreous

Identified July 27, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: brownish-grey with slight translucency; Luster: waxy to vitreous; Crystal structure: trigonal (microcrystalline); Cleavage: none, conchoidal fracture

Formation & geological history

Formed by the precipitation of silica-rich solutions in cavities of sedimentary or volcanic rocks. Over time, erosion rounds these silica nodules into smooth stream or beach pebbles.

Uses & applications

Used in lapidary work for tumbling, polishing, and crafting small beads or cabochons. Also collected by rockhounds.

Geological facts

Chalcedony is composed of fine intergrowths of quartz and moganite. Translucent varieties are often classified as agate or jasper depending on their banding and opacity.

Field identification & locations

Identified by its smooth, waxy feel, translucency when backlit, hardness (scratches glass), and lack of cleavage. Commonly found along riverbeds, beaches, and gravel deposits worldwide.