Formula: CaSO4.2H2O Monoclinic
Description:
Gypsum is a relatively common mineral in a number of environments. It is found in sedimentary rocks, either as a primary precipitate from sea or saline lake waters or as a alteration of minerals such as anhydrite. It is deposited from groundwater with sedimentary rocks such as shale or limestone. Gypsum also forms from low temperature hydrothermal fluids. It can form during the weathering of sulfides such as marcasite.
BROWN COUNTY: Gypsum occurs as small clear crystals in shale at Whitney’s Bluff in Green Bay (Irving, 1883). Gypsum nodules are also found in calcareous mudstones of the Scales Shale within the county. (Steiglitz and Allen, 1980).
CALUMET COUNTY: Crowns (1976) notes that gypsum is found as colorless crystals within the county.
DOOR COUNTY: Irving (1883) reports gypsum in drift fragments and small crystals in bedrock near Sturgeon Bay. Sherrill (1978) finds that gypsum occurs with chert in dolostone at the base of the Alexandrian series near the contact with the Maquoketa Shale throughout the county.
FOND DU LAC COUNTY: Sprays of micro gypsum crystals occur in the pyritiferous shale of the Reedstown Member exposed in an Fairweather Quarry, SW NE Sec. 36 T.15N R.13E, SW of Ripon (UWO, 1994).
IOWA COUNTY: Delicate acicular sprays of gypsum crystals occur with smithsonite, galena and marcasite in the zinc-lead mines near Mineral Point (Raasch, 1924). Some of these crystals are 1 cm. long and in clusters as much as 4 cm. across (Milwaukee Public Museum specimens). Hobbs (1895) describes some of these crystals in detail and found them elongated parallel to the c axis, with {010}, {111} and {hk0} dominating. Hobbs also believes that much of the materials labeled “anglesite” from zinc-lead ore are, in reality, gypsum.
IRON COUNTY: Gypsum occurs in the Cary, Montreal and other mines of the Gogebic iron range (Dickey, 1938). At the Montreal Mine clear euhedral crystals occur with hematite, goethite, barite, celestine and calcite in vugs within the Ironwood Iron Formation (LaBerge, 1984). Also selenite masses reportedly big as a house filled vugs in the Montreal Mine, and were removed with cross-cut saws. (Barlow, 1997).
LAFAYETTE COUNTY: Found within the mines of the zinc-lead district within the county Heyl et. al. (1959). reports acicular white crystals coating the mine walls along with pale green melanterite stalactites in the lower levels of the Little Giant Mine, near Shullsburg (E 1/2 SW Sec. 4 T.1N R.2E).
MANITOWOC COUNTY: Clear striated gypsum crystals and cleavable masses occur in vugs in limestone with marcasite and calcite in the Rockwood Quarry, near Manitowoc (Zeitner, 1988, Steiglitz, personal comm., 1990). Good specimens are stored in the Milwaukee County Public Museum. Zeitner (1988) also reports gypsum found “near Francis Creek”.
PIERCE COUNTY: Pond (1964) reports gypsum flowers as occurring at Crystal Cave. The current owners of the cave, Jean and Blaze Cummingham, the two geologists who currently own and operate the cave, could not confirm this report.
RACINE COUNTY: Gypsum occurs as micro crystals. in vugs in limestone at the Vulcan Materials (old Ives) Quarry. Associated minerals are calcite, strontianite, pyrite, marcasite and sphalerite (Scovil, 1994).
ROCK COUNTY: Gypsum is found as an alteration product of pyrite within the St. Peter Formation in the silica sand quarry near Hanover. Associated minerals include alunite, jarosite and lepidochrocite (Odom, Willard and Lassin, 1979). This association is likely widespread in the state.
RUSK COUNTY: Gypsum crystals occur with dolomite, ankerite and sulfides in a carbonate zone within the Flambeau Copper Mine, Ladysmith. (Cordua, field notes).
— Gypsum occurs with anhydrite, antigorite and carbonate in an unusual mafic meta-tuff at the Eisenbrey massive sulfide deposit, north of Ladysmith (May, 1996).
WOOD COUNTY: Gypsum occurs as micro -xls. rosettes with siderite in veins in granite at the Haske Quarry, Cary Bluffs, Sec. 25 T.24N. R.2E. (Buchholz, 1997, personal communication).