Fossiliferous Limestone

Physical Properties

Hardness: 3 on Mohs scale; Color: Tan, beige, grey, and cream; Luster: Dull to earthy; Crystal structure: Hexagonal/Trigonal (calcite); Cleavage: Perfect rhombohedral in calcite matrix; Specific gravity: 2.71

Formation & Geological History

Formed in shallow marine environments where organic debris like shells, corals, and algal remains accumulate and are compressed over millions of years. This specimen appears to contain brachiopod or bivalve imprints common from the Paleozoic to Mesozoic eras.

Uses & Applications

Used primarily in construction (crushed stone, cement manufacturing), as a building material, in agriculture for soil conditioning, and as educational or decorative specimens for collectors.

Geological Facts

Limestone contains roughly 10% of the total volume of all sedimentary rocks. The presence of shells in this rock indicates it was once part of an ancient seafloor.

Field Identification & Locations

Identify in the field by the visible presence of fossilized shells or casts and by testing with diluted hydrochloric acid; limestone will effervesce (fizz). Commonly found in areas with past marine history like the Midwest United States or the UK.

Identified on: 4/13/2026

Mode: Standard