sedimentary

Limestone ( weathered ) / Chert Nodular Rock

Sedimentary rock (primarily Calcium Carbonate, CaCO3, with Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 3 for limestone matrix, 7 for chert nodules. Color: Buff, light brown, tan to yellowish. Luster: Dull, earthy. Structure: Fine-grained, non-crystalline appearance, highly weathered exterior. Specific gravity: 2.5 - 2.7.

Hardness: 3 for limestone matrix, 7 for chert nodules
Color: Buff, light brown, tan to yellowish
Luster: Dull, earthy

Identified July 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in shallow, warm marine environments through the accumulation and compaction of organic debris or chemical precipitation of calcium carbonate, often containing chert nodules or silica inclusions. Weathering has given it a rough, buff-colored outer rind.

Uses & applications

Commonly used in construction, crushed stone aggregate, road base, soil conditioning (lime), cement manufacturing, and building material.

Geological facts

Weathered limestone and chert often form nodules that can host internal hollows or geodes. Limestone makes up about 10% of the total volume of all sedimentary rocks globally.

Field identification & locations

Identify in the field by checking if it effervesces (fizzes) with dilute hydrochloric acid. It can often be scratched with a steel nail if pure limestone, or resist scratching if silicified/cherty. Found abundantly worldwide in sedimentary rock basins.