sedimentary
Chert / Flint Nodules in Limestone
Silicon Dioxide (SiO2) within Calcium Carbonate (CaCO3)
Hardness: 7 (Chert) / 3 (Limestone); Color: Gray to Tan; Luster: Waxy to Dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture in chert); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Chert) / 3 (Limestone)
- Color
- Gray to Tan
- Luster
- Waxy to Dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Chert) / 3 (Limestone); Color: Gray to Tan; Luster: Waxy to Dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture in chert); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through chemical precipitation where silica replaces carbonate minerals in sedimentary beds, often in deep-sea environments or via groundwater during diagenesis.
Uses & applications
Used historically for stone tools (weapons/scrapers). Industrial uses include decorative landscaping, concrete aggregate, and silicon production.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its use in flintlock firearms. It is chemically identical to quartz but contains microscopically small crystals.
Field identification & locations
Identify in the field by checking for a smooth, waxy texture that is much harder than the surrounding porous rock. Common in the midwestern USA and the Chalk cliffs of Europe. Collectors look for colorful variants like Jasper or Agate.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite (primarily SiO2)
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