sedimentary
Sandstone with Iron Oxide Concretion
Arenite with Hematite/Goethite Concretion
Hardness: 6-7 (quartz matrix), Color: Tan to light brown with a dark brown/black circular spot, Luster: Dull/Earthy, Structure: Granular/Clastic with a nodular inclusion
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Physical properties
Hardness: 6-7 (quartz matrix), Color: Tan to light brown with a dark brown/black circular spot, Luster: Dull/Earthy, Structure: Granular/Clastic with a nodular inclusion
Formation & geological history
Formed via the accumulation of sand-sized grains, later cementation, and the localized precipitation of iron-rich minerals from groundwater into a concretion during diagenesis.
Uses & applications
Primarily of interest to collectors or as a decorative curiosity; sandstone itself is widely used in construction and landscaping.
Geological facts
These 'bullseye' rocks occur when minerals like hematite or goethite concentrate in a specific spot within the porous sandstone, often starting around a small organic nucleus.
Field identification & locations
Identify by the distinct color contrast and circular pattern; commonly found in riverbeds, beaches, and desert regions like the Southwestern United States.
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