sedimentary

Tumbled iron-rich concretion or ironstone pebble

Goethite–hematite-rich ironstone; commonly limonite (FeO(OH)·nH₂O) with hematite (Fe₂O₃)

AI-generated identification · may be incorrect

Dark brown to black, opaque, earthy to submetallic luster, smoothly water-worn or tumbled, with faint fibrous/striated textures. Hardness is approximately 5–6.5 Mohs; no obvious cleavage; specific gravity commonly 3.0–4.3.

Identified August 26, 2026More sedimentary →

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At a glance

Common name: Tumbled iron-rich concretion or ironstone pebble
Scientific name: Goethite–hematite-rich ironstone; commonly limonite (FeO(OH)·nH₂O) with hematite (Fe₂O₃)
Category: sedimentary
Identified: August 26, 2026
Method: Standard

AI Estimated Value

About $2–$15 for a common tumbled pebble; $20–$75 if unusually patterned, dense, or locality-provenance is documented.

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

Likely formed as an iron-oxide/hydroxide concretion or weathering product that became rounded in sediment or stream transport; exact age and locality cannot be determined from the image. Ironstones form in many sedimentary and lateritic environments.

Uses & applications

Primarily a collector or teaching specimen; ironstone is mined as iron ore, while attractive polished pieces may be used decoratively. It is generally not a jewelry gemstone.

Geological facts

Its unusually heavy appearance and rusty-brown color reflect concentrated iron minerals. The surface pattern may result from botryoidal or fibrous goethite growth and subsequent polishing.

Field identification & locations

Test for strong heft, streak, and possible magnetism; a yellow-brown streak suggests goethite/limonite, while a red-brown streak suggests hematite. Common in iron-rich soils, river gravels, and banded-iron regions worldwide.