sedimentary

Banded Chert / Mookaite Jasper

Microcrystalline Quartz (SiO2)

Mohs hardness of 6.5 to 7. Shows smooth conchoidal fracture with a dull to waxy luster. Features opaque bands of mustard yellow, purplish-grey, and tan. Microcrystalline (cryptocrystalline) structure without visible cleavage. Specific gravity around 2.65.

Identified July 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation and precipitation of silica-rich fluids and radiolarian/diatomaceous sediments in marine or groundwater environments. Iron oxides and trace elements impart the distinct yellow, purple, and red coloration.

Uses & applications

Used for lapidary work, cabochon cutting, polished ornamental stones, carvings, and popular as a decorative display specimen for rock collectors.

Geological facts

Chert has been used since prehistoric times to produce sharp edges for stone tools like arrowheads and knives due to its reliable conchoidal fracture pattern. Color variations are often driven by varying degrees of iron oxidation.

Field identification & locations

Identified by its dense, smooth texture, lack of visible mineral grains, waxy surface, and sharp shell-like (conchoidal) fractures. Widely found in sedimentary rock formations, stream beds, and coastal deposits globally, with famous vibrant varieties found in Western Australia.

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