Chert / Jasper Cobble

Hardness: 6.5-7 Mohs. Color: Reddish-brown, tan, and dark grey-brown. Luster: Dull to earthy on weathered surfaces, waxy to sub-vitreous on fresh fractures. Fracture: Conchoidal to sub-conchoidal. Specific Gravity: 2.58-2.64.

Formed via biochemical or chemical precipitation of silica in ocean or freshwater sedimentary environments. Over time, original silica oozes consolidate into microcrystalline quartz nodules or beds, often enriched with iron oxide impurities that produce reddish-brown hues. This specimen has been rounded into a cobble by water or glacial transport.

Commonly used historically by indigenous peoples for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today it is used for gravel, landscaping, lapidary tumbling, and educational collecting.

Jasper and chert are essentially the same microcrystalline silica rock; when rich in iron oxide producing opaque reds, browns, or yellows, it is typically classified as jasper. The water-worn smooth surface indicates it was gathered from a riverbed, stream, or glacial till deposit.

Identify in the field by its hardness (scratches glass easily, cannot be scratched by a steel pocketknife), smooth water-worn exterior, and characteristic smooth/curved conchoidal fracture surfaces. Common in riverbeds, gravel pits, and ancient sedimentary formations worldwide.