Limonite is not a single mineral species but a field-name for amorphous to cryptocrystalline iron hydroxide aggregates — primarily goethite and lepidocrocite mixtures with adsorbed water. It forms massive earthy yellow-brown to dark brown deposits in lateritic weathering profiles, bog iron deposits, and the gossan caps of Fe-bearing sulfide deposits.
Key Facts
- Mohs hardness 4–5.5 (variable).
- Amorphous to cryptocrystalline mixture — not a single species.
- Yellow-brown to dark brown earthy color.
- Common pigment (“yellow ochre”) used since prehistoric times.
- Pseudomorphs after pyrite, marcasite, siderite are collector classics.
Notable Localities
Bog iron deposits worldwide. Quincy mining district (Michigan) and Lake Superior region host iconic limonite gossans.
