sedimentary
Chert (Jasper/Agate variety)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: White, cream, and reddish-orange; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic crystals); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 Mohs
- Color
- White, cream, and reddish-orange
- Luster
- Waxy to vitreous
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 Mohs; Color: White, cream, and reddish-orange; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microscopic crystals); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich fluids in limestone or volcanic host rocks, often as nodules or replacement layers. These specimens are commonly found along the shores of the Great Lakes, originally deposited during the Paleozoic era.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp conchoidal fracture. Currently used for lapidary work, jewelry, tumbling, and as a collector's specimen.
Geological facts
This specimen appears to be a piece of chert or 'pudding stone' matrix, common to the Lake Michigan area. Native Americans highly valued this material for its durability and predictable breaking patterns when flintknapping.
Field identification & locations
Identify in the field by its waxy texture and shell-like (conchoidal) fractures. It will easily scratch glass. Commonly found on Great Lakes beaches as rounded pebbles or angular fragments.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary