sedimentary

Chert (Jasper/Flint variant)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 7 (Mohs scale); Color: Tan, brown, and yellowish-brown; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, and yellowish-brown
Luster: Waxy to dull

Identified April 1, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. This specimen appears to be a weathered nodule, potentially from Paleozoic to Mesozoic era deposits.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modernly used in road surfacing, decorative landscaping, and occasionally lapidary work if highly colorful.

Geological facts

Chert is so durable that it often survives as 'river gravel' long after the surrounding limestone or chalk has eroded away. Iron oxide impurities are what give this specific piece its yellowish-brown 'butterscotch' hue.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture patterns and ability to scratch glass. It often has a smooth, waxy texture and often occurs as rounded nodules in stream beds or embedded in limestone.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary