sedimentary

Boxwork Siderite or Sepatarian Nodule Weathering

Siderite (FeCO3) with secondary mineralization or Boxwork Geode fragment

AI-generated identification · may be incorrect

Hardness: 3.5-4.5 (Mohs), Color: Earthy brown to tan, Luster: Dull or earthy, Structure: Amorphous/microcrystalline matrix with raised mineral ridges, Cleavage: None visible in hand specimen.

Hardness: 3

Identified March 15, 2026More sedimentary →

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Physical properties

Hardness: 3.5-4.5 (Mohs), Color: Earthy brown to tan, Luster: Dull or earthy, Structure: Amorphous/microcrystalline matrix with raised mineral ridges, Cleavage: None visible in hand specimen.

Formation & geological history

Formed through chemical precipitation in sedimentary basins where mineral-rich fluids fill cracks (dessication or tectonic) in mudstone or clay. As the softer surrounding rock erodes, the harder mineral-filled veins remain, creating a 'boxwork' pattern.

Uses & applications

Primarily used as display specimens for hobbyist geologists; historically, siderite has been used as a minor iron ore.

Geological facts

This cellular pattern is often mistaken for fossils such as turtle shells or bone fragments, but it is a purely geological phenomenon where mineral veins resist weathering more effectively than the host rock.

Field identification & locations

Identify in the field by the raised, crisscrossing ridges that form geometric enclosures (cells). Commonly found in areas with eroded claystone or shale beds, such as badlands or creek beds.