sedimentary

Chert (Yellow Jasper/Common Opal variety)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Honey yellow to orange-brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Honey yellow to orange-brown
Luster: Waxy to vitreous

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Honey yellow to orange-brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in sedimentary basins or volcanic cavities. Often occurs as nodules or beds within limestone or volcanic rocks.

Uses & applications

Commonly used for lapidary work, jewelry (cabochons), and historically for stone tools due to its sharp conchoidal fracture.

Geological facts

Yellow jasper and chert were often used by indigenous peoples for arrowheads and scrapers. The coloration usually comes from trace inclusions of goethite or iron oxides.

Field identification & locations

Identified in the field by its waxy luster, smoothness, and the way it breaks into sharp, curved flakes (conchoidal fracture). It cannot be scratched by a steel knife. Common in river beds and gravel pits.