sedimentary

Chert (specifically Jasper or Flint variant)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Brown, yellowish-tan with dark inclusions, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified May 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like radiolarians or diatoms) or through the chemical precipitation of silica in groundwater. This often occurs in limestone or chalk beds. This specimen likely formed during the Paleozoic or Mesozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads/knives) due to its sharp conchoidal edges; currently used for gem cutting (lapidary), as a grinding media in ball mills, and for road surfacing or gravel.

Geological facts

Chert has been used by humans for over 2 million years to create tools. When struck with steel, it can produce sparks, which led to its extensive use in flintlock firearms.

Field identification & locations

Identified in the field by its hardness (scratches glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) fracture patterns. Frequently found in riverbeds or as nodules in limestone outcrops.

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