sedimentary

Fossiliferous Limestone (Crinoidal)

Calcite-bearing bioclastic packstone (CaCO3)

Hardness: 3 (Mohs). Color: Grey to tan with white circular fossil inclusions. Luster: Dull/Earthy. Structure: Massive/Fine-grained with visible fossil fragments. Cleavage: Perfect rhombohedral in calcite crystals, though often hidden in matrix.

Hardness: 3 (Mohs)
Color: Grey to tan with white circular fossil inclusions
Luster: Dull/Earthy

Identified May 21, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in warm, shallow marine environments through the accumulation of organic debris (specifically crinoid stem fragments and shells) on the sea floor during the Paleozoic era (approx. 300-450 million years ago).

Uses & applications

Primarily used in construction (aggregate, cement), as architectural stone, and for educational/collecting purposes due to fossil content.

Geological facts

The circular white rings are cross-sections of crinoids, also known as 'sea lilies,' which were echinoderms related to modern starfish. When they died, their stacked skeletal columns broke apart into 'cheerio-shaped' discs.

Field identification & locations

Identify in the field by checking for the presence of fossil cross-sections and performing an acid test (it will fizz with weak hydrochloric acid/vinegar). Commonly found in limestone outcrops and riverbeds globally.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary