Limonite Concretion (Pseudometeorite)
Goethite/Limonite mixture (Amorphous or Cryptocrystalline) · Mineral Specimen / Decorative Stone
Crystal System
Amorphous/Cryptocrystallline; typically lacks visible crystal faces, appearing massive or earthy.
Mineral Group
Oxides / Hydroxides (Iron-bearing minerals)
Chemical Formula
FeO(OH)·nH2O (Hydrated iron oxide)
Formation Process
Sedimentary/Hydrothermal; formed via the oxidation and hydration of iron-rich sulfide minerals or precipitation from iron-rich groundwater.
About This Crystal
An opaque, dull, brownish-grey or dark-grey stone with a heavy, metallic appearance. It features smooth, rounded 'thumbprint' depressions similar to regmaglypts, though likely caused by differential weathering.
Physical Characteristics
Color: Dark greyish-brown; Streak: Yellowish-brown; Luster: Dull to sub-metallic; Specific Gravity: 2.7–4.3; Fracture: Uneven to sub-conchoidal; non-magnetic.
Optical Properties
Opaque; No refractive index (RI) measurable without polished surface; no pleochroism or dispersion.
Hardness & Durability
Origin Region
Found globally in sedimentary basins; notable for 'ironstone' nodules in desert or fluvial environments.
Hardness & Durability
Mohs Hardness: 4.0 - 5.5; Brittle tenacity; generally stable but can be porous.
Care & Maintenance
Gently clean with warm water and soft brush; avoid acids which can dissolve iron oxides; store in dry conditions to prevent further oxidation.
Rarity & Value
Common; frequently mistaken for meteorites by laypeople. Low commercial value unless containing rare internal fossils.
Special Characteristics
Features 'regmaglypt-like' indentations and a high density compared to common rocks; lacks the Widmanstätten patterns or fusion crust of true meteorites.
Lore & History
Historically used as iron ore and pigment (ochre). In folklore, such stones are often called 'thunderstones' and were believed to fall from the sky or provide grounding energy.