White aragonite crystals up to 2 mm long with unknown black mineral. From the Flambeau Mine in Ladysmith, Rusk County, Wisconsin. (Photo by Dan Behnke.)

Formula: CaCO3 Orthorhombic


Aragonite forms in low temperature hydrothermal deposits, especially as sinter around hot springs and amygdules in basalts. It also occurs as speleothemes, as organic or inorganic precipitates in marine sediments. Finally, it forms by high pressure low temperature metamorphism such as is found in subduction zones. It inverts in geologically short time periods to calcite.

DODGE COUNTY: Reported with biohermal material in the dolostones of the Burnt Bluff Group as exposed in the quarry near Nasbro at center Sec.18 T.13N R.17E (Soderman and Carozzi, 1963).

IOWA COUNTY: Found as acicular white xls. 0.1 to 1 cm long in Roger’s Cave, SW NW NE Sec. 17 T.7N R.3E, north of Dodgeville (Poster, 1966).

LAFAYETTE COUNTY: Reported as a rare secondary mineral in the zinc-lead deposits in the Belmont and Calamine Quadrangles (Klemic and West, 1964).

RUSK COUNTY: Forms as acicular crystals on calcite in the carbonate zone at the Flambeau Mine, near Ladysmith.