sedimentary
Ironstone Concretion (Moqui Marble)
Iron-oxide concretion (Fe2O3 / FeO(OH))
Hardness: 5-5.5 (outer shell); Color: Dark brown to reddish-brown; Luster: Submetallic to earthy; Structure: Spheroidal/Concentric; Cleavage: None; Specific Gravity: 3.4-5.0
- Hardness
- 5-5
- Color
- Dark brown to reddish-brown
- Luster
- Submetallic to earthy
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Physical properties
Hardness: 5-5.5 (outer shell); Color: Dark brown to reddish-brown; Luster: Submetallic to earthy; Structure: Spheroidal/Concentric; Cleavage: None; Specific Gravity: 3.4-5.0
Formation & geological history
Formed through the precipitation of iron-bearing minerals (hematite or goethite) from groundwater within porous sandstone layers, often around a small nucleus like a sand grain or fossil. Typically associated with Jurassic period formations (like the Navajo Sandstone).
Uses & applications
Primarily used as metaphysical stones, educational specimens for geology, and occasionally used as a source of iron ore in historical contexts.
Geological facts
Commonly known as Moqui Marbles or Shaman Stones, these are found in large concentrations in the American Southwest and are famous for their perfectly spherical shapes which can range from marble-sized to cannonball-sized.
Field identification & locations
Identify by their round shape and heavy weight relative to size. Found in eroded sandstone plateaus. Collectors should look for a hard, dark crust covering a lighter sandy core.
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