GLAUCONITE (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2 Monoclinic

Description: Glauconite is abundant in the Paleozoic sandstones in Wisconsin where it forms rounded dark green sand-sized nodules. At places glauconite may make up the majority of the rock, forming what are commonly called ":greensands". It may be intergrown with, associated with and confused with chlorites such as, chamosite or clay minerals such as celadonite. Glauconite is considered diagnostic of sediments deposited in a continental shelf marine environment. It is suggestive of slow rates of sediment accumulation and may form by biogenetic or diagenetic alteration of minerals such as biotite or volcanic glass.

glauconite

Sandstone with abundant dark green glauconite grains. Hudson, St. Croix County, WI.

In Wisconsin glauconite forms thick beds within the Cambrian Lone Rock Group and is also found in lesser amounts in the Mt. Simon Sandstone, Eau Claire Formation and Wonewoc Formation. It can on occasion be found in many other Paleozoic clastic units in the state. Only a few representative localities for the mineral will be described below.

BUFFALO COUNTY: Glauconite is abundant in the sandstones of the Lone Rock Formation exposed along the access road to the Parker Limestone Quarry, 5 miles south of Mondovi on County Trunk ZZ, NE NW sec. 35 T.23N. R.11W. (Kopp and Willis, 1974).

CRAWFORD COUNTY: Glauconite is abundant in the Lone Rock Formation exposed near Boscobel (Twenhofel, 1936).

DANE COUNTY: Glauconite is abundant in the rocks of the Lone Rock formation exposed in Mazomonie Bluff, along Hwy. 14 on the east edge of Mazomonie (NE SE NW sec. 16 T.8N. R.6E.) (Odom, 1978a, Ostrum, WGNHS outcrop description.)
Glauconite occurs in greensands in the Maple Bluff area on the north shore of Lake Mendota, near Madison. (Twenhofel, 1936).

EAU CLAIRE COUNTY: Glauconite is abundant in the outcrops of the Lone Rock Formation exposed in a roadcut on Route 93, NE NW Sec. 19 T.25N. R.9W, near Mondovi. (Kopp and Willis, 1974).

IOWA COUNTY: Glauconite is abundant in the Lone Rock Formation exposed in roadcuts along Hwy 133 along the south shore of the Wisconsin River near Lone Rock , NW SW SE sec. 13 T.8N. R.2E. (Odom, 1978).

JACKSON COUNTY: Glauconite is abundant in the Lone Rock Formation exposed in a borrow pit on the south side of Pine Creek Road, NW sec. 10 T.21N. R.5W. It can be found in similar circumstances near the radio tower in sec. 22 T.22N R.4W.and the lookout tower in NE sec33 T.22N. R.1W. (Klemic and Ohlson, 1973).

LACROSSE COUNTY: Glauconite occurs in the Lone rock formation exposed at the base of Grandfather Bluff and elsewhere along the Mississippi Valley near LaCrosse (Twenhofel, 1936).

MONROE COUNTY: Glauconite is abundant in greensands exposed near Norwalk and Tunnel City. (Twenhofel, 1936).

PEPIN COUNTY: Glauconite-rich greensands are exposed along in stream and highway cuts north of Arkansaw (W.S.C. field notes.)

ST. CROIX COUNTY: Glauconite-rich greensands are exposed along Coulee Road near Birkmoose Park in downtown Hudson. (W.S.C., field notes). SAUK COUNTY: Glauconite is abundant in cuts along the abandoned railroad tracks west of the Wisconsin Hwy. 136 bridge over the Baraboo River north of Rock Springs (R. Paull, personal comm.).

TREMPEALEAU COUNTY: Glauconite is abundant in the Lone Rock Formation exposed in roadcuts along County D, north of Whitehall in SW SW sec. 12 T.22N. R.8W. (Ostrum, W.G.N.H.S. outcrop descriptions).
- Glauconite is abundant in the Lone Rock Formation exposed in roadcuts along Hwy 53, at Decorah Peak,1.2 miles east of Galesville SW SE sec. 34 T.19N. R.8W (Ostrum, W.G.N.H.S. outcrop descriptions).

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