sedimentary
Chert (Jasper/Agate)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Dark grey with yellowish/tan inclusions (eye-like pattern). Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Dark grey with yellowish/tan inclusions (eye-like pattern)
- Luster
- Waxy to vitreous
Identified More sedimentary →
Explore Chert (Jasper/Agate) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Dark grey with yellowish/tan inclusions (eye-like pattern). Luster: Waxy to vitreous. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. The smooth, rounded shape suggests it is a water-worn river stone or a tumbled specimen.
Uses & applications
Used for jewelry (cabochons), lapidary art, flintknapping (historically for tools), and as landscaping stone.
Geological facts
This specific piece is often called an 'eye stone' or 'orbital chert' due to the circular inclusion. Chert is extremely durable and was one of the primary materials used by prehistoric people for arrowheads.
Field identification & locations
Identify by its hardness (will scratch glass), smooth waxy feel, and characteristic shell-like (conchoidal) fractures. Often found in riverbeds, glacial till, or limestone outcrops.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Brown Sandstone (River Rock)
Arenite
sedimentary
Mudstone
Argillite / Siliciclastic sedimentary rock
sedimentary
Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary