sedimentary
Moqui Marble (Concretion)
Iron Oxide Concretion (Hematite/Goethite)
Hardness: 5-6 (outer shell); Color: dark brown to black exterior, tan/sand interior; Luster: dull to sub-metallic; Crystal Structure: Amorphous/Microcrystalline; Specific Gravity: 3.4-5.0.
- Hardness
- 5-6 (outer shell)
- Color
- dark brown to black exterior, tan/sand interior
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 5-6 (outer shell); Color: dark brown to black exterior, tan/sand interior; Luster: dull to sub-metallic; Crystal Structure: Amorphous/Microcrystalline; Specific Gravity: 3.4-5.0.
Formation & geological history
Formed by the precipitation of iron oxide minerals from groundwater flowing through porous sandstone layers, often during the Jurassic or Cretaceous periods. The minerals cement sand grains together around a central nucleus.
Uses & applications
Primarily collected as geological curiosities and metaphysical stones. Used in small-scale lapidary work and educational displays.
Geological facts
Also known as Navajo Cherries or Hopi Marbles, they are frequently found in the Navajo Sandstone of Utah. Similar 'blueberries' were discovered on Mars by the Opportunity rover, suggesting a history of water on the red planet.
Field identification & locations
Identify by their distinct spherical shape, dark iron-rich crust, and sandy core. They are often found weathering out of sandstone cliffs or lying in 'fields' on the desert floor.
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