sedimentary

Chert or chalcedony fragment

Microcrystalline quartz (SiO₂), possibly jasper or agate

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; pale cream, gray, and reddish-brown banding with a dull to waxy luster. It has cryptocrystalline quartz structure, no visible cleavage, and typically conchoidal fracture; the apparent triangular shape may be naturally fractured or human-shaped.

Identified August 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in sedimentary rocks, often producing iron-oxide colors and banding. The specimen’s exact geological age cannot be determined from the image; chert and chalcedony occur from Precambrian to modern deposits.

Uses & applications

Used for sharp-edged tools, decorative stone, beads, cabochons, and lapidary carvings; attractive banded pieces may have modest jewelry or collector value.

Geological facts

Chert can produce exceptionally sharp flakes because of conchoidal fracture. Red coloration commonly comes from hematite or other iron oxides.

Field identification & locations

Test cautiously for glass-like hardness: it should scratch ordinary glass and leave a white streak on unglazed ceramic; inspect for waxy texture and curved fracture surfaces. Common worldwide, especially in limestone and volcanic terrains.