Bayfield Group

The Bayfield group is a quartz sandstone found in Wisconsin along the Lake Superior coast. It is named for the village of Bayfield, Wisconsin, but was once known as Western Lake Superior Sandstone.

Prior to the 1900s, Bayfield group sandstone was also variously named Lake Superior Sandstone, brownstone, or redstone, and prefixed by the quarry location. The name was changed to the Bayfield group as its relation to Jacobsville Sandstone (once known as Lake Superior Sandstone) is uncertain.

The Bayfield group is irregularly bedded, in contrast to the even, calcareous sandstones in southern Wisconsin. The geological formation is entirely devoid of fossils. The Bayfield group overlies the much thicker Oronto Group.

The formation, 4300 feet thick, is divided into three: Chequamegon Sandstone, Devils Island Sandstone, and Orienta Sandstone. The Chequamegon Sandstone is a red and white sandstone 1000 feet thick. The Devils Island Sandstone is a 300-foot thick, pink-to-white pure quartz sandtone with significant ripples. The Orienta Sandstone is 3000 feet thick and similar to the Chequamegon Sandstone, but with a higher feldspar concentration.

The Bayfield group is a member of the Keweenawan Supergroup.

The Bayfield group is a predominantly red sandstone, though it varies through lighter colors such as pink, yellow, light brown, gray and white. A minority portion is a dark "brownstone" which is a good building material. The colors occur in bands, though mottling and other irregular markings are common.

As most of the stone's constituents are the end-products of weathering, it is very resistant to atmospheric action.

The grains vary from coarse pebbly grits to shale. The finer the grains, the darker their color. The grains are cemented primarily by quartz, with iron oxide coating the grains.

In order of abundance, the Bayfield group is composed of: quartz, feldspar (both orthoclase and plagioclase), mica, iron oxide (both magnetite and limonite), chert, and ferromangesian minerals. The quartz usually comprises about 75% of the stone.

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