sedimentary
Chert (specifically Tan/Gray Chert)
Microcrystalline quartz (SiO2)
Hardness: 7 (Mohs); Color: Tan, brownish-gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- Tan, brownish-gray
- Luster
- Waxy to dull
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 (Mohs); Color: Tan, brownish-gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or by the precipitation of silica from groundwater within sedimentary rock layers, often limestone.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; used today in road construction aggregate and sometimes as a minor gemstone when colorful (Jasper).
Geological facts
Chert has a conchoidal fracture, which means it breaks like glass. This property made it the primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), waxy appearance, and shell-like fracture patterns. Common in limestone outcrops and riverbeds.
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