sedimentary
Chert with Limestone matrix
Microcrystalline silica (SiO2) in Calcite (CaCO3) matrix
Hardness: 7 for chert, 3 for limestone; Color: Gray, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture in chert)
- Hardness
- 7 for chert, 3 for limestone
- Color
- Gray, tan, and creamy white
- Luster
- Waxy to dull
Identified More sedimentary →
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Physical properties
Hardness: 7 for chert, 3 for limestone; Color: Gray, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture in chert)
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation within marine limestone beds. Common in many geological periods where marine environments existed.
Uses & applications
Historically used for making stone tools; currently used as aggregate, decorative stone, and by rockhounds for lapidary work.
Geological facts
The chert part of this specimen is significantly harder than the surrounding limestone and will scratch glass. Chert nodules often preserve microfossils.
Field identification & locations
Identified by its waxy luster and distinctive conchoidal (shell-like) fracture patterns on broken gray surfaces. Commonly found in limestone outcrops, riverbeds, and gravel pits.
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