sedimentary
Chert (Jasper/Agate variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: tan, reddish-brown, and gray; Lustre: waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6 - 2.65
- Hardness
- 6
- Color
- tan, reddish-brown, and gray
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 on Mohs scale; Color: tan, reddish-brown, and gray; Lustre: waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed through the precipitation of silica-rich fluids within sedimentary rock cavities or by the accumulation of siliceous organisms like diatoms and radiolaria. Often found in limestone or as nodules in soil/landscaping rock.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges when broken. Currently used for decorative landscaping, lapidary work (polishing), and as a gemstone (jasper/agate varieties).
Geological facts
This specimen appears to be a water-worn or weathered nodule. Because it is microcrystalline, it breaks with a conchoidal fracture, similar to glass, which is why it was the primary material for prehistoric toolmaking.
Field identification & locations
Identify in the field by its waxy texture, smooth conchoidal fractures, and hardness (it will scratch glass). Commonly found in stream beds, gravel pits, and landscaping mulch. This specific piece shows a mix of chalcedony and jasper-like coloration.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary