sedimentary

Orbicular jasper (orbicular chert)

Silica-rich microcrystalline quartz, SiO₂; orbicular jasper/chert with concentric silica bands

AI-generated identification · may be incorrect

Cream, tan, and brown concentric orbicules in an opaque, fine-grained stone; quartz hardness about 6.5–7 Mohs, vitreous to waxy luster, no visible crystals or cleavage. The specimen appears rough and naturally broken.

Identified October 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Silica-rich fluids can replace or cement sedimentary material, forming concentric growth or replacement patterns. Such rocks formed in varied settings and ages; the exact origin and age cannot be determined from the photo alone.

Uses & applications

Used for lapidary work, cabochons, beads, and decorative objects; attractive patterned pieces are collected.

Geological facts

The circular patterns are orbicules—concentric bands that may form through mineral growth or replacement, rather than being fossil shells.

Field identification & locations

Look for hard, opaque material with repeated circular bands; it should scratch glass and resist scratching from a steel knife. Orbicular jasper and chert occur in multiple regions, but a locality cannot be established from appearance alone.