sedimentary
Chert (specifically Flint or Nodular Chert)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Brown, dark grey, or black with a waxy/dull luster. Features conchoidal fracture (breaks like glass) and microcrystalline structure. Very dense and non-porous.
- Color
- Brown, dark grey, or black with a waxy/dull luster
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Physical properties
Hardness: 7 (Mohs scale), Color: Brown, dark grey, or black with a waxy/dull luster. Features conchoidal fracture (breaks like glass) and microcrystalline structure. Very dense and non-porous.
Formation & geological history
Formed by the precipitation of silica from seawater or groundwater. Commonly occurs as nodules in limestone or chalk beds. Often associated with Cretaceous or Carboniferous period deposits.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Today used for ignition sources (flint and steel), road surfacing, and as a raw material for silicon-based products.
Geological facts
Chert has been used by humans for hundreds of thousands of years due to its ability to be chipped into extremely sharp edges. It is chemically identical to quartz but contains impurities that produce its earthy colors.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture pattern and high hardness (it will scratch glass). Often found in riverbeds or weathered out of sedimentary cliffs. Look for smooth, waxy surfaces on broken edges.
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