Biogenic Chert
“Silica from a billion tiny lives”
Biogenic chert is a hard, microcrystalline silica rock formed from the accumulated siliceous skeletons of marine organisms like radiolarians, diatoms, and sponge spicules. Over millions of years, these delicate glass structures dissolve and reprecipitate as dense, incredibly hard chert layers.
microcrystalline quartz (chalcedony), opal, radiolarian/diatom remains, clay minerals (minor)
Monterey Formation (California, USA), Danish chalk cliffs (flint nodules), Japan (ribbon cherts), Franciscan Complex (California)
6.5-7
The famous flint tools of prehistoric humans were made from biogenic chert — every hand axe and arrowhead was ultimately crafted from the compressed remains of trillions of microscopic sea creatures.
Test Your Knowledge
How did prehistoric flint tools connect to biogenic chert's microscopic origins?
Photo Attribution
Title: Keokuk Chert (Keokuk Formation, Lower Mississippian; midwestern USA) 4.jpg
Author: James St. John
License: CC BY 2.0
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