sedimentary
Chert (Common Opal/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: White, tan, pinkish-hues; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
- Hardness
- 6
- Color
- White, tan, pinkish-hues
- 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 scale); Color: White, tan, pinkish-hues; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6
Formation & geological history
Formed through the precipitation of silica from groundwater in sedimentary host rocks or from the accumulation of siliceous skeletal remains of microscopic organisms. This specimen appears to be associated with volcanic or limestone environments where silica replaced original minerals.
Uses & applications
Used historically for stone tools and arrowheads; currently used as ornamental stones, lapidary lapidary rough for tumbling, or as a decorative component in landscaping.
Geological facts
Chert and its variants like jasper and flint were the most important minerals for early human survival due to their predictable fracturing into razor-sharp edges. Some pinkish varieties in the desert are often called 'Desert Jasper' or 'Common Opal' depending on hydration levels.
Field identification & locations
Identify in the field by its waxy texture and conchoidal (shell-like) fracture patterns. It is extremely hard and will scratch glass and steel. Commonly found in desert regions of the American Southwest within limestone or rhyolite deposits.
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