sedimentary
Chert (Arrowhead)
Chert (primarily Microcrystalline Silica, SiO2)
Hardness: 7 Mohs scale; Color: Tan, beige, or brownish; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Tan, beige, or brownish
- 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 scale; Color: Tan, beige, or brownish; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater in sedimentary rock layers like limestone or chalk. While the rock itself is millions of years old, this specimen was worked into a projectile point during various archaeological time periods.
Uses & applications
Historically used for making stone tools and weaponry due to its sharp edges; modernly used as a collectible artifact and in lapidary work.
Geological facts
Chert and its variety, flint, were among the most critical materials for early humans. It breaks with a conchoidal fracture, creating razor-sharp edges ideal for cutting and hunting.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fracture marks where it has been chipped or flaked. Common in limestone-rich regions and frequently found in riverbeds or tilled fields.
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