mineral

Iron-rich weathered rock, possibly limonite/goethite-bearing breccia

Limonite (FeO(OH)·nH₂O), goethite (α-FeO(OH)), and iron oxides; host uncertain

AI-generated identification · may be incorrect

Earthy, porous, and strongly multicolored with red-brown, yellow, greenish, and bluish surface coatings. Likely low-to-moderate hardness (about 4–5.5), dull to earthy luster, and no obvious cleavage; exact properties require testing.

Identified September 14, 2026More mineral →

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At a glance

Common name: Iron-rich weathered rock, possibly limonite/goethite-bearing breccia
Scientific name: Limonite (FeO(OH)·nH₂O), goethite (α-FeO(OH)), and iron oxides; host uncertain
Category: mineral
Identified: September 14, 2026
Method: Standard

AI Estimated Value

About $1–$15 as a common weathered specimen; higher only if testing confirms attractive copper mineralization or a collectible locality.

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

Probably formed by oxidation and weathering of iron-bearing rock or sulfide minerals, producing hydrated iron oxides and secondary coatings. The reported Marin County, California area commonly contains weathered volcanic, sedimentary, and serpentinite-related rocks, but the specimen’s exact source is uncertain.

Uses & applications

Usually a cabinet or curiosity specimen; limonite/goethite may serve as an iron ore or natural pigment, but this small piece has little industrial value.

Geological facts

Red, yellow, and brown colors are typical of hematite and goethite/limonite. Green-blue areas could reflect copper minerals, serpentinite, or staining, but they are not identifiable confidently from the photograph.

Field identification & locations

Streak on unglazed porcelain is diagnostic: yellow-brown suggests limonite/goethite, red-brown suggests hematite. Check magnetism, specific gravity, and whether dilute hydrochloric acid reacts; avoid assuming copper minerals without chemical testing.