sedimentary
Brachiopod Fossil in Chert
Phylum Brachiopoda within Microcrystalline Quartz (SiO2)
Hardness: 7 (matrix); Color: Tan to reddish-brown (iron staining); Luster: Dull to waxy; Structure: Fan-like shell impressions with radial ribbing; High resistance to weathering.
- Hardness
- 7 (matrix)
- Color
- Tan to reddish-brown (iron staining)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (matrix); Color: Tan to reddish-brown (iron staining); Luster: Dull to waxy; Structure: Fan-like shell impressions with radial ribbing; High resistance to weathering.
Formation & geological history
Formed through the fossilization of marine organisms in silica-rich sedimentary environments, typically during the Paleozoic era (approx. 250-500 million years ago). The silica replaced or encased the original calcium carbonate shell.
Uses & applications
Primarily used for geological study, paleontological collecting, and educational purposes. Some high-quality fossiliferous chert is used for lapidary work or flintknapping.
Geological facts
Brachiopods look like clams but are biologically distinct; they are 'lamp shells' that use a lophophore to filter feed. They were one of the most abundant life forms on Earth before the Permian-Triassic extinction.
Field identification & locations
Identify in the field by looking for distinctive fan-shaped symmetry and radial ridges (costae) within hard, flint-like nodules. Frequently found in riverbeds, gravel pits, and limestone outcroppings across the Midwest USA and UK.
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