Redgranite Quarry

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

SE 1/4 SW 1/4 Sec 8, T18N R12E, in Redgranite on State Route 21. Park behind the bank where Route 21 makes a 45-degree bend to the left.

The rock is uniform fine-grained pink granite of the 1700 m.y. old rhyolite-granite suite. A flooded quarry, popular with scuba divers because of its great depth. A footpath leads around the quarry.

Views of the Quarry



The Dike

A mafic dike cuts across the quarry and stands up on both sides as a low wall. Here we see the south side of the quarry looking along the dike to the north side.
The dike on the north side of the quarry. The dike is the vertical rock sticking out of the water.
The contact between the pink granite (right) and the bluish dike (left) bisects the picture. Note the drillhole astride the contact.

Small-Scale Features

The quarry is a nice place to observe small-scale brittle fracture, glacial, and aeolian features.

Brittle Fracture Features

Plumose fracturing is well-exposed on many fracture faces
This small splaying joint suggests left-lateral shear.

Glacial and Aeolian Features

Chatter marks (this picture and below) are common. As is typical for localities on the western margins of the Green Bay Lobe, they suggest westward movement of ice away from the lobe axis rather than southward motion.
A glacially polished and striated surface.
Signs of wind abrasion are common on crystalline rock outcrops in Wisconsin, but frequently not noticed. Typical indicators are smooth, sometimes polished, but pitted surfaces. With abundant sand, strong katabatic winds and little vegetation, Wisconsin during ice retreat was an ideal environment for wind abrasion.

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Created 19 September 2000, Last Update 12 Jan 2020