Marcasite Concretions (Wisconsin)

These little rocks are Concretions found in southeast Wisconsin. They are composed of dolomite (a sedimentary rock) and marcasite (a sulfide mineral). They are brown with a slight iridescent sheen, in overall round shapes with smooth or globular texture on the outer surface. Four sizes available: Price:  $14.99 $19.99 $24.99 $29.99 Size (approx): 1.25" x 1" x 1" 1.5" x 1.5" x 1" 2" x 1.5" x 1" 2.5" x 1.5" x 1.25" Weight Range: 1oz - 3oz 2oz - 4oz 5oz - 8oz 7oz - 10oz Pictured with a quarter for size reference Concretions are a type of geological formation created through mineral precipitation around some type of nucleus within sedimentary rock. Inside buried sediment, as the mineral precipitates outward it acts as a glue with the surrounding material, cementing it together. The mass is then slightly harder than the sediment around it and over time this creates this nodule-like appearance. Concretions are more resistant to weathering than the sedimentary rock they formed in, so they are often found exposed at the surface or even fully dislodged from their host rock.