sedimentary

Calcite-rich limestone with iron-oxide staining and a possible concretion

Calcite (CaCO₃) in micritic limestone; brown coating likely goethite/limonite

AI-generated identification · may be incorrect

Soft, pale cream to tan, earthy to pearly surfaces; calcite has Mohs hardness 3, rhombohedral cleavage, and vitreous-to-pearly luster, while the matrix appears fine-grained and irregular. The rounded brown nodule is likely an iron-rich concretion or weathering rind.

Identified August 24, 2026More sedimentary →

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At a glance

Common name: Calcite-rich limestone with iron-oxide staining and a possible concretion
Scientific name: Calcite (CaCO₃) in micritic limestone; brown coating likely goethite/limonite
Category: sedimentary
Identified: August 24, 2026
Method: Standard

AI Estimated Value

About $5–$25 as a common hand specimen; potentially $30–$75 if locality-provenanced or unusually aesthetic.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Formed from compacted carbonate mud or shell debris, later altered and stained by iron-bearing groundwater; commonly Cenozoic to Paleozoic depending on locality. The concretion developed during or after burial as minerals cemented a localized zone.

Uses & applications

Limestone is widely used for cement, aggregate, lime, dimension stone, and soil treatment; attractive calcite specimens are collected but this example appears mainly educational rather than gem-quality.

Geological facts

Calcite vigorously effervesces with dilute hydrochloric acid, distinguishing it from many similar pale rocks. Iron oxides produce the yellow-brown coloration through oxidation of iron-bearing fluids.

Field identification & locations

Likely identification can be tested by a vinegar or dilute acid reaction, though vinegar may be weak, and by scratching with a steel nail. Common in limestone quarries, caves, road cuts, and sedimentary outcrops worldwide.