sedimentary
Chert (within Limestone matrix)
Silicon Dioxide (SiO2) within Calcium Carbonate (CaCO3)
AI-generated identification · may be incorrectChert: Hardness 7 (Mohs), waxy to dull luster, conchoidal fracture, various tan/brown shades. Limestone: Hardness 3, dull luster, light gray/white, fizzes with acid.
Identified More sedimentary →
Explore Chert (within Limestone matrix) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Chert: Hardness 7 (Mohs), waxy to dull luster, conchoidal fracture, various tan/brown shades. Limestone: Hardness 3, dull luster, light gray/white, fizzes with acid.
Formation & geological history
Formed by the accumulation of microcrystalline silica often in marine environments within carbonate sediments. The light gray host rock is limestone, while the orange-brown nodule is chert, formed via chemical replacement.
Uses & applications
Historically used for stone tools (arrowheads). Today used for landscaping, aggregate in construction, and as a geological study specimen.
Geological facts
Chert nodules like this one are often harder than the surrounding limestone, causing them to protrude as the limestone weathers away. Chert has been used by humans for millions of years to start fires and make sharp tools.
Field identification & locations
Identify in the field by checking for the conchoidal (curved, shell-like) fracture on the brown portion and its ability to scratch glass. Found globally in limestone layers.
More like this
Other sedimentary specimens
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Quartz pebble
Silicon dioxide (SiO2)
sedimentary
Generic Pebble / Rock Fragment
Lithic fragment / Weathered rock
sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary