sedimentary

Fossiliferous limestone pebble

Bioclastic limestone, chiefly calcite (CaCO₃)

AI-generated identification · may be incorrect

Dark gray-green, rounded and water-worn, with pale fossil or shell fragments in a fine-grained matrix and a dull to slightly waxy surface. Calcite has Mohs hardness 3 and rhombohedral cleavage; the rock’s hardness varies, and dilute acid may fizz on fresh surfaces.

Identified September 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed as carbonate mud and shell fragments accumulated in a shallow marine setting, then compacted and cemented; the pebble’s age cannot be determined from the image. The reported Guerrero-area location is geologically plausible for marine sedimentary rocks, though the exact source is uncertain.

Uses & applications

Limestone is used for cement, aggregate, building stone, and agricultural lime; this small pebble is mainly of interest as a possible fossil-bearing specimen.

Geological facts

The light markings resemble bioclasts, but the photograph alone cannot confirm that they are fossils rather than mineral grains or other inclusions.

Field identification & locations

Look for recognizable shell patterns and test a fresh spot with dilute hydrochloric acid (with appropriate safety precautions); calcite-rich limestone fizzes. Rounded edges suggest transport in water. Similar rocks occur widely in marine sedimentary formations.