sedimentary
Chert (Common Opal/Agate mixture)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Variegated red, white, grey, and yellow; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Variegated red, white, grey, and yellow
- Luster
- Waxy to vitreous
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 Mohs; Color: Variegated red, white, grey, and yellow; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed via the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids in volcanic ash beds and limestone cavities. Often associated with Tertiary period volcanic activity.
Uses & applications
Used for lapidary work (cabs and polishing), aquarium decor, historical tool making (knapping), and as a collectible landscape rock.
Geological facts
The red coloring is typically caused by inclusions of iron oxides (hematite). Because it breaks with a conchoidal fracture like glass, it was a primary material for prehistoric arrowheads and scrapers.
Field identification & locations
Identify by its sharp, glass-like edges when broken, waxy texture, and inability to be scratched by a steel knife. Commonly found in Oregon and the American Southwest in desert washes.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary