sedimentary
Oolitic Chert
Silicon Dioxide (SiO2) with oolitic texture
Hardness: 7 (Mohs scale), Color: tan, grey, or white; Luster: waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Conchoidal fracture; unique texture composed of small rounded spheres (ooliths).
- Hardness
- 7 (Mohs scale), Color: tan, grey, or white
- Color
- tan, grey, or white
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, grey, or white; Luster: waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Conchoidal fracture; unique texture composed of small rounded spheres (ooliths).
Formation & geological history
Formed in warm, shallow, wave-agitated marine environments where calcium carbonate ooids were precipitated and later replaced by silica (chertification) during diagenesis.
Uses & applications
Used primarily as archaeological indicators, road aggregate, and for decorative lapidary work. It was historically used for making stone tools due to its hardness and sharp fracture edges.
Geological facts
The term 'oolith' comes from the Greek word 'oion', meaning egg, referring to the rock's resemblance to fish roe. Some oolitic cherts are famous for preserving microscopic Precambrian fossils.
Field identification & locations
Identify in the field by looking for a hard, silica-rich rock that scratches glass and features tiny, perfectly round concentric spheres on a weathered surface. Commonly found in limestone-rich geological formations in the Midwest USA.
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