sedimentary

Oolitic Limestone / Fossiliferous Chert

Oolitic Limestone (CaCO3) / Silicified Limestone

Hardness: 3-4 for limestone, 7 for chert/silicified; Color: Gray, tan, buff; Luster: Dull to earthy; Texture: Granular appearance with small rounded 'ooids' or fossil imprints; Specific Gravity: 2.3-2.7

Hardness: 3-4 for limestone, 7 for chert/silicified
Color: Gray, tan, buff
Luster: Dull to earthy

Identified April 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in warm, shallow, wave-washed marine environments where calcium carbonate precipitates around a nucleus, or through the replacement of limestone by silica. Most common in Paleozoic to Mesozoic era deposits.

Uses & applications

Used in construction as a building stone, in the production of cement, as a decorative stone in jewelry (if polished), and for the study of ancient marine environments.

Geological facts

The name 'Oolite' comes from the Greek word 'oion' for egg, describing its resemblance to fish roe. Major formations include the Cotswolds in England and parts of the Midwestern United States.

Field identification & locations

Identify by looking for small, spherical grains (ooids) or concentric pits on a weathered surface. It will typically react (fizz) with dilute hydrochloric acid if it is still limestone; silicate versions will not.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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