sedimentary

Chert (Yellow Jasper)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Yellow, mustard, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Yellow, mustard, ochre
Luster: Waxy to dull

Identified July 6, 2026More sedimentary →

Explore Chert (Yellow Jasper) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Yellow, mustard, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich groundwater within sedimentary beds. The yellow color typically comes from iron oxide (goethite) inclusions.

Uses & applications

Used historically for stone tools due to its sharp edges when fractured; modernly used for lapidary work, jewelry (cabochons), and as aquarium stones.

Geological facts

Chert and jasper have been used by humans for over a million years to create spearheads and arrowheads because they fracture predictably with very sharp 'razor' edges.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and its shell-like (conchoidal) fracture pattern. It is commonly found in limestone and chalk deposits globally.