sedimentary
Chert (Flint Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: brownish-grey, tan, and olive hues; Luster: waxy to dull; Fracture: conchoidal; Crystal system: trigonal (microcrystalline/cryptocrystalline).
- Hardness
- 7 on Mohs scale
- Color
- brownish-grey, tan, and olive hues
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: brownish-grey, tan, and olive hues; Luster: waxy to dull; Fracture: conchoidal; Crystal system: trigonal (microcrystalline/cryptocrystalline).
Formation & geological history
Formed in marine environment sedimentary rock formations, primarily through the accumulation of silica-rich biogenic ooze (from radiolarians and diatoms) that dissolved and recrystallized within limestone or chalk beds.
Uses & applications
Historically used for stone tools, arrowheads, and flintlock firearms. Today it is used in decorative landscaping, construction aggregate, and as a subject for amateur rock collecting.
Geological facts
Chert and flint were among the earliest raw materials utilized by prehistoric humans to forge sharp tools because of their predictable, razor-sharp conchoidal fracture patterns.
Field identification & locations
Identified by its high hardness (scratches glass readily), smooth to waxy feel, and characteristic shell-like (conchoidal) fracture edges. Commonly found in gravel beds, chalk cliffs, and river deposits worldwide.
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