Limonite (Ironstone) Concretion
Goethite/Limonite with Quartz inclusions · Mineral Specimen / Sedimentary Rock
Crystal System
Amorphous or Orthorhombic (Goethite), typically massive or botryoidal habit
Mineral Group
Oxides and Hydroxides
Chemical Formula
FeO(OH)·nH2O (Hydrated Iron Oxide)
Formation Process
Sedimentary precipitation where iron-rich groundwater cements minerals around a nucleus
About This Crystal
Opaque, dark brown to blackish-brown exterior with a dull to sub-metallic luster and a rough, pitted surface texture featuring white secondary mineral inclusions.
Physical Characteristics
Yellowish-brown streak, no cleavage, uneven to conchoidal fracture, specific gravity 2.7–4.3, non-fluorescent.
Optical Properties
Opaque; light does not pass through even on thin edges; no birefringence or pleochroism visible.
Hardness & Durability
Origin Region
Worldwide; notably Southwestern USA (Moaki Marbles types) and Australia (Ironstone)
Hardness & Durability
Mohs 4 to 5.5; brittle and prone to scratching; stability is high unless exposed to strong acids.
Care & Maintenance
Clean with a dry brush or damp cloth; avoid ultrasonic cleaners and aggressive chemicals; store dry to prevent further oxidation.
Rarity & Value
Very common; low commercial value as a gemstone; valued primarily as a geological curiosity or for landscape use.
Special Characteristics
May contain 'concretions' or 'nodules' morphology; the white spots are likely trapped calcite or quartz mineralizations.
Lore & History
Historically used as brown iron ore; traditionally associated with grounding and protection in folklore due to its density and earth-based origin.