mineral

Chalcedony / Agate Pebble

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Purple, lavender, white, gray; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None, conchoidal fracture

Hardness: 6
Color: Purple, lavender, white, gray
Luster: Waxy to vitreous

Identified July 22, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Purple, lavender, white, gray; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None, conchoidal fracture

Formation & geological history

Formed via precipitation of silica-rich solutions within cavity vesicles of volcanic rocks or sedimentary environments over millions of years, later weathered out and rounded by water transport.

Uses & applications

Lapidary work, tumbling, jewelry beads, cabochons, and rock collecting.

Geological facts

Agate and chalcedony are cryptocrystalline varieties of quartz. Purple shades often come from trace iron or manganese impurities within the silica matrix.

Field identification & locations

Look for waxy luster, smooth water-worn surface with subtle translucency, and conchoidal fractures. Commonly found on riverbanks, beaches, and gravel beds.