sedimentary
Chert (Nodule)
Chert (variety of microcrystalline quartz, SiO2)
Hardness: 7 (Mohs scale), Color: Dark brown, black, and reddish-brown, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs scale), Color: Dark brown, black, and reddish-brown, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich marine organisms. Often found as nodules within limestone or chalk beds. Period range varies from Precambrian to current.
Uses & applications
Historically used for making stone tools (flintknapping); currently used as an abrasive, decorative stone in landscaping, or as a gemstone if colorful (Jasper).
Geological facts
Chert is so hard it can scratch steel. It was one of the most important materials for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and spears.
Field identification & locations
Identify by its extreme hardness, waxy appearance, and smooth, curved shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or within sedimentary rock formations.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary