sedimentary
Chert (flint), likely a knapped fragment
Microcrystalline quartz (SiO₂), also called cryptocrystalline quartz
AI-generated identification · may be incorrectUsually Mohs 6.5–7; this specimen is dark gray-brown with a dull to waxy surface and sharp, curved conchoidal fractures. Its microscopic quartz crystals are too small to see individually; cleavage is absent.
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Physical properties
Usually Mohs 6.5–7; this specimen is dark gray-brown with a dull to waxy surface and sharp, curved conchoidal fractures. Its microscopic quartz crystals are too small to see individually; cleavage is absent.
Formation & geological history
Forms when silica precipitates or replaces material in sedimentary rocks, commonly limestone or chalk. The image cannot establish its age; chert occurs in sedimentary deposits of many geological periods.
Uses & applications
Used historically for stone tools and fire-starting, and today for decorative objects and some specialized industrial applications.
Geological facts
The flake-like scars and razor-sharp edges suggest it may have been deliberately struck or knapped, though the photo alone cannot confirm human workmanship.
Field identification & locations
Look for very fine grain, hardness, and smooth, curved fracture surfaces; it commonly occurs as nodules or layers in limestone and chalk. Found worldwide, including flint-bearing chalk regions.
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