Knowra Chert Chert Chert is a hard, fine-grained sedimentary rock composed mainly of microcrystalline quartz. It forms through silica accumulation and replacement, often involving microscopic marine organisms.
Quartz : Quartz is a crystalline mineral composed of silicon dioxide, SiO₂. Chert is made chiefly of quartz in crystals too small to see individually.
Siliceous ooze : Siliceous ooze is deep-sea sediment dominated by the silica remains of microscopic organisms. Its buried shells can dissolve, migrate, and reprecipitate as chert.
Radiolarite : Radiolarite is a siliceous sedimentary rock formed chiefly from accumulated radiolarian remains. It is a biologically derived chert whose texture and fossils record pelagic deposition.
Lithic reduction : Lithic reduction is the shaping of stone by removing flakes to produce tools or other forms. Archaeologists identify chert artifacts through the flakes and fracture surfaces produced during shaping.
Jasper : Jasper is an opaque, fine-grained variety of silica-rich rock, commonly colored by iron oxides. Jasper resembles chert in composition but is distinguished chiefly by its color and opacity.
Silica : Silica is silicon dioxide, a compound found in minerals, rocks, and dissolved forms. Dissolved silica supplies the material that accumulates or replaces sediment to form chert.
Diagenesis : Diagenesis comprises the physical and chemical changes that transform sediment into sedimentary rock. Silica dissolution, movement, and precipitation during burial create many chert deposits.
Diatomite : Diatomite is a soft, porous sedimentary rock composed mainly of diatom shells. It shares a biological silica source with some chert but remains porous and weakly consolidated.
Flintknapping : Flintknapping is the controlled shaping of stone by striking or pressing off flakes. Chert’s sharp, conchoidal fractures make it suitable for this craft.
Agate : Agate is a banded variety of chalcedony, a microcrystalline form of silica. Its conspicuous concentric banding separates agate from typically massive chert.
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