sedimentary
Chert (with Manganese Dendrites)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs); Color: White to grey with dark brown/black surface staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.65.
- Hardness
- 7 (Mohs)
- Color
- White to grey with dark brown/black surface staining
- 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: White to grey with dark brown/black surface staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); SG: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich microfossils (like radiolarians or diatoms) or chemical precipitation of silica in ocean floor sediments. The dark patterns are manganese oxides that precipitated into cracks or onto the surface.
Uses & applications
Historically used for stone tools/arrowheads. Currently used as industrial abrasive, landscaping gravel, and as educational or decorative lapidary specimens.
Geological facts
This specimen shows manganese oxide staining which often creates 'dendrites'—branching tree-like patterns that are frequently mistaken for plant fossils. Chert is the parent material for jasper and flint.
Field identification & locations
Identify by its hardness (will scratch glass), conchoidal (shell-like) fracture, and smooth, waxy texture. Commonly found in riverbeds and coastal regions where ancient sedimentary layers have eroded.
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