sedimentary
Jasper or Chert with Quartz Vugs
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and grey with white quartz patches; Luster: Dull to waxy, vitreous in quartz areas; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brown, tan, and grey with white quartz patches
- Luster
- Dull to waxy, vitreous in quartz areas
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: Brown, tan, and grey with white quartz patches; Luster: Dull to waxy, vitreous in quartz areas; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the precipitation of silica from groundwater filling cavities (vugs) in limestone or volcanic ash. The brown color comes from iron oxide impurities. These can range from millions to hundreds of millions of years old depending on the host formation.
Uses & applications
Commonly used for lapidary work (cabs or tumbling), decorative garden stones, and as a collector specimen. Historically used for making tools like scrapers or arrowheads due to its hardness and sharp edges.
Geological facts
This specimen appears to be 'vuggy,' meaning it has small cavities filled with secondary minerals, likely quartz or calcite. Silica-rich rocks like this are extremely resistant to weathering, which is why they are often found as loose stones in riverbeds.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its waxy texture. It is often found in areas with sedimentary limestone or ancient volcanic activity. Collectors should look for the 'sparkle' of small crystals in the recessed areas.
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