sedimentary
Piddock bored rock (Boring Stone)
Ichnofossil-bearing Limestone or Mudstone (trace fossils by Pholadidae)
Hardness: 3-4 (matrix), Color: Tan to grey, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None. Notable for smooth, cylindrical or teardrop-shaped holes bored into the surface.
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Physical properties
Hardness: 3-4 (matrix), Color: Tan to grey, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None. Notable for smooth, cylindrical or teardrop-shaped holes bored into the surface.
Formation & geological history
Formed through bioerosion where marine bivalves (Piddocks) use their shells to rasp circular burrows into soft sedimentary rocks on the seafloor or intertidal zones. Geological age is usually Holocene to Pleistocene for surface finds.
Uses & applications
Primarily used as decorative display pieces for collectors, educational specimens for ichnology (the study of trace fossils), or as garden ornaments.
Geological facts
The holes are created by living organisms, not natural erosion or bubbles. Piddocks spend their entire lives inside these holes, getting larger as the hole gets deeper, eventually becoming trapped inside.
Field identification & locations
Identify by looking for perfectly circular or oval holes that taper inward on marine sedimentary rocks. Often found on beaches in coastal regions like the UK, California, or the Mediterranean.
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