sedimentary
Chalk
Microcrystalline calcite (CaCO3)
AI-generated identification · may be incorrectHardness 1 on Mohs scale, white to light gray color, dull to earthy luster, fine-grained amorphous crystal structure, specific gravity around 1.5 to 2.1.
Identified More sedimentary →
Explore Chalk in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness 1 on Mohs scale, white to light gray color, dull to earthy luster, fine-grained amorphous crystal structure, specific gravity around 1.5 to 2.1.
Formation & geological history
Formed from the accumulation of microscopic calcareous shell remains of marine organisms like coccolithophores during the Cretaceous period.
Uses & applications
Used in agriculture for soil conditioning, manufacturing lime and cement, writing chalk, and industrial fillers.
Geological facts
Chalk deposits formed the famous White Cliffs of Dover and give the Cretaceous period its name from the Latin word for chalk, creta.
Field identification & locations
Identified by its soft, powdery texture and vigorous effervescence when exposed to dilute hydrochloric acid. Found globally in marine sedimentary basins.
More like this
Other sedimentary specimens
Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
fossil
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite
sedimentary
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary