mineral
Likely limonite/goethite-rich ironstone
Limonite (amorphous hydrated iron oxides), commonly mixed with goethite, hematite, and host rock
AI-generated identification · may be incorrectBrown to black, earthy to submetallic luster, irregular botryoidal or cavernous surfaces; typically non-crystalline to microcrystalline. Mohs hardness about 4–5.5, specific gravity roughly 3.0–4.3; may leave a yellow-brown streak and is often weakly magnetic if magnetite is present.
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Physical properties
Brown to black, earthy to submetallic luster, irregular botryoidal or cavernous surfaces; typically non-crystalline to microcrystalline. Mohs hardness about 4–5.5, specific gravity roughly 3.0–4.3; may leave a yellow-brown streak and is often weakly magnetic if magnetite is present.
Formation & geological history
Forms through weathering and oxidation of iron-bearing minerals, commonly as botryoidal or cavity-filling masses in soils, hydrothermal veins, and sedimentary iron deposits. It is generally geologically young relative to its source rock and may form at any age.
Uses & applications
Used historically as an iron ore and yellow-brown pigment; attractive pieces are collected, though it is not typically used as a gemstone. Common specimens usually sell for about $5–$30, with unusual botryoidal or locality specimens reaching $50–$150.
Geological facts
The specimen’s rusty brown coloration and irregular masses strongly suggest hydrated iron oxides, but the photograph cannot distinguish limonite from goethite or iron-rich breccia confidently.
Field identification & locations
Look for yellow-brown streak, earthy texture, high density, and rusty coatings; a streak test, magnet test, and hardness test help distinguish it from basalt or slag. Common in oxidized zones, laterite, bog-iron deposits, and weathered ore bodies.
