sedimentary
Chert (Greenish-Grey variety)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dull greenish-grey with slight translucency; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Dull greenish-grey with slight translucency
- Luster
- Waxy to vitreous
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Dull greenish-grey with slight translucency; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from seawater or the accumulation of siliceous biological remains (like diatoms or radiolarians). It often occurs as nodules or layers in limestone or shale and can range from Precambrian to modern ages.
Uses & applications
Historically used for stone tools and starting fires (flint); currently used as abrasive media, road surfacing aggregate, and occasionally for lapidary work in jewelry.
Geological facts
Chert was a primary technology for early humans due to its conchoidal fracture which produces razor-sharp edges. It is chemically identical to quartz but contains impurities that give it various colors.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy appearance, and sharp, curved fracture patterns. Common in marine sedimentary basins and riverbeds as smoothed pebbles.
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