sedimentary

Chert (Jasper/Agate variety)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: White, cream, and reddish-orange; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic crystals); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 Mohs
Color: White, cream, and reddish-orange
Luster: Waxy to vitreous

Identified June 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich fluids in limestone or volcanic host rocks, often as nodules or replacement layers. These specimens are commonly found along the shores of the Great Lakes, originally deposited during the Paleozoic era.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp conchoidal fracture. Currently used for lapidary work, jewelry, tumbling, and as a collector's specimen.

Geological facts

This specimen appears to be a piece of chert or 'pudding stone' matrix, common to the Lake Michigan area. Native Americans highly valued this material for its durability and predictable breaking patterns when flintknapping.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) fractures. It will easily scratch glass. Commonly found on Great Lakes beaches as rounded pebbles or angular fragments.