sedimentary
Chert (Fossiliferous)
Microcrystalline quartz (SiO2)
Hardness: 7 on the Mohs scale, Color: White, cream, and yellowish-tan, Luster: Vitreous to dull, Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony), Cleavage: None (exhibits conchoidal fracture), Specific Gravity: 2.60-2.65.
Identified More sedimentary →
Explore Chert (Fossiliferous) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on the Mohs scale, Color: White, cream, and yellowish-tan, Luster: Vitreous to dull, Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony), Cleavage: None (exhibits conchoidal fracture), Specific Gravity: 2.60-2.65.
Formation & geological history
Formed through the diagenesis of silica-rich marine sediments, often involving the replacement of limestone or chalk by silica from sponge spicules or radiolaria over millions of years.
Uses & applications
Historically used for making stone tools and arrowheads due to its sharp conchoidal fracture. Today used locally for decorative landscaping or collected as a geological specimen.
Geological facts
Chert containing fossils often displays distinctive small circular pits or impressions where ancient marine organisms or fossil fragments have weathered out.
Field identification & locations
Can be identified in the field by its high hardness (scratches glass), waxy to dull luster, and smooth conchoidal fracture. Frequently found in limestone and chalk formations worldwide.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Quartz pebble
Silicon dioxide (SiO2)
sedimentary
Generic Pebble / Rock Fragment
Lithic fragment / Weathered rock
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Banded Siltstone / Mudstone Pebble
Siltstone / Argillite
sedimentary