sedimentary
Ironstone Concretion (Moqui Marble)
Ferruginous Concretion (Fe2O3 / FeO(OH))
Hardness: 5-5.5 on Mohs scale; Color: Dark brown, reddish-brown, or tan; Luster: Dull/Earthy; Crystal structure: Amorphous or Microcrystalline; Specific Gravity: Approx 3.0-4.0
- Hardness
- 5-5
- Color
- Dark brown, reddish-brown, or tan
- Luster
- Dull/Earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-5.5 on Mohs scale; Color: Dark brown, reddish-brown, or tan; Luster: Dull/Earthy; Crystal structure: Amorphous or Microcrystalline; Specific Gravity: Approx 3.0-4.0
Formation & geological history
Formed through the precipitation of iron oxide minerals from groundwater within sandstone or shale beds, often around a central nucleus such as a fossil or pebble. Most common in Mesozoic formations like the Navajo Sandstone.
Uses & applications
Used primarily as decorative specimens for collectors, metaphysical 'shaman stones', and occasionally crushed for iron ore or as pigment.
Geological facts
These are often called 'Moqui Marbles' in Southwestern United States; they can range from the size of a pea to several meters across. They have an iron-rich outer shell and often a softer sandstone core.
Field identification & locations
Identify by its spherical or ellipsoidal shape, heavy weight for its size, and rusty/dark appearance; found frequently in arid desert environments where errosion exposes them in sandstone layers.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Sandstone
Arenite
sedimentary