sedimentary
Fossilized Crab Carapace (Concretion)
Decapoda (fossil), typically preserved in calcite or siderite concretion
Hardness: 3-5 (Mohs), Color: Tan, brown, or grey earthy tones, Luster: Dull/Earthy, Crystal Structure: Amorphous (microcrystalline matrix), often featuring bilateral symmetry of a crab shell.
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Physical properties
Hardness: 3-5 (Mohs), Color: Tan, brown, or grey earthy tones, Luster: Dull/Earthy, Crystal Structure: Amorphous (microcrystalline matrix), often featuring bilateral symmetry of a crab shell.
Formation & geological history
Formed when a crab carcass settles in soft mud; minerals precipitate around the organic matter, hardening into a concretion over millions of years (often Eocene or Miocene epochs).
Uses & applications
Educational purposes, scientific research, and high value for fossil collectors.
Geological facts
Many of the world's best crab fossils are found inside 'nodules' or concretions that must be carefully split or prepared with pneumatic tools to reveal the anatomy inside.
Field identification & locations
Look for rounded, heavy stones in sedimentary layers or beaches. Identification is based on the visible bump patterns (nodes) and the distinct shape of the crab's shell (carapace).
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