Athelstane and Amberg Granites: These granites come from nearby towns in northeastern Wisconsin, just south of the Michigan border. They are similar in grain size, but the Amberg is more gray, whereas the Athelstane is more pink. They both formed as intrusive bodies of rock that formed the core or subsurface of volcanic islands some 1840-1890 million years ago, when northern Wisconsin looked more like the Japanese Islands do today. These granites were a few of many granites quarried in Wisconsin. In fact Red Granite is the State rock. Today one can visit a small museum in Amberg, which documents the local quarry industry. You are encouraged to see some of the rock in its “natural” state at the Joe Davies county park just off Highway 141 near Amberg.
Bedford Limestone: This sedimentary rock is formally known as the Salem Limestone, but also simply as Indiana Limestone. It is quarried in south central Indiana between Bloomington and Bedford. It was originally deposited in a warm shallow marine environment during Mississippian time (320-360 million years ago). The fine oolitic texture would suggest the sediments were subjected to wave action and marine currents sufficient to winnow the fossil fragments to a uniform size. If one looks closely at the stone you will see it is composed almost entirely of small fragments of marine shells. The Salem Limestone has been used extensively for buildings for over 100 years because of its uniform texture and ease of working. It is fairly soft and can easily be shaped with carving tools.
Berea Sandstone: This sandstone comes primarily from north-central Ohio in the vicinity of Berea, near Cleveland. The sandstone is part of the Bedford-Berea sedimentary sequence, which extends from Pennsylvania to Kentucky. It is of Mississippian age, but slightly older than the Bedford Limestone. The quarry stone is thickly bedded and frequently shows depositional structures such as cross bedding, and current ripples. Its uniform texture over great thickness and ease of cutting into dimensional stone has made it a prized building material for over 100 years.
Bethel White: This coarse grained igneous rock is a type of granitic rock that is specifically identified as a quartz monzonite. It is quarried near the town of Bethel, Vermont. The Vermont granitic rocks are much younger than the rest of the granitic rocks seen in this field trip. The age of this rock is ~335 m.y. which places it in the middle of the Mississippian Period (mid Paleozoic Era).
Carnelian Granite: This coarse-grained igneous rock is a true granite of Early Proterozoic age (about 2000 m.y.). It is quarried near the town of Milbank, South Dakota. The main minerals evident in the rock are quartz, potassium feldspar, plagioclase feldspar,and biotite. Trace amounts of zircon, apatite and hornblende also occur. The rock also displays “myrmekite”, a wart-like growths of plagioclase and quartz that extends into neighboring potassium feldspar grains. This distinctive feature typically occurs during the later stages of the crystallization process.
For those of you who are petrologists, this rock contains anomalously high amounts of strontium and zinc. It appears to have formed from an andesitic rock at just above the minimum melting temperature.
Diamond Pink: This porphyritic igneous rock is a true granite of Early Proterozoic age (1700-1800 m.y.). It is quarried near the town of St. Cloud Minnesota. The main minerals evident in the rock are quartz, potassium feldspar, plagioclase feldspar,and biotite. Smaller amounts of zircon, apatite, hornblende, chlorite and sericite also occur. The potassium feldspars are the large crystals (“phenocrysts”) set in an otherwise equi-granular matrix.
Hallowell and Fox Island Granite: The Hallowell Granite is a coarse-grained igneous rock that is primarily a biotite-muscovite granite. It was quarried in the town of Hallowell, Maine near the banks of the Kennebec River. The rock crystallized 380-390 m.y. ago, which places it in the middle Devonian. The main minerals evident in the rock are white orthoclase feldspar, quartz, biotite and muscovite. The overall color is very white with a uniformly fine-grained texture. The Fox Island Granite is a very similar rock quarried on the Fox Island near the mouth of the Sheepscot River.
Joliet Limestone: This rock is another Silurian age building stone of the Midwest. Its primary source is a quarry in Batavia, Illinois, which is just west of Chicago near Aurora. The stone is also known as Joliet Marble and Athens Marble, although it is not marble. These other names indicate that similar rock was quarried in those nearby towns. It tends to weather to a buttery yellow color which is not true of Waukesha Dolomite quarried in Wisconsin.
Lac Du Bonnet: This coarse grained igneous rock is a type of granitic rock that is specifically identified as a quartz monzonite. It is quarried near the town of Pinawa, Manitoba Canada. The rock crystallized 2700 m.y. ago, which places it in the Late Archaean. The main minerals evident in the rock are potassium feldspar, plagioclase feldspar, quartz, sericite, biotite, and muscovite. Smaller amounts of chlorite, epidote, zircon and apatite also occur. The presence of minerals such as sericite and chlorite indicate that the rock has undergone a phase of secondary alteration after it initially crystallized.
For those of you who are petrologists, this rock contains relatively high amounts of uranium and thorium. Being a quartz monzonite (or adamellite), the rock contains intermediate amounts of the alkali elements (sodium and potassium) and calcium. The extrusive equivalent is rhyodacite.
Lake Superior Sandstone: This sandstone that is mostly red or brown in color comes primarily form the Bayfield Group of sedimentary rocks that are found near Bayfield, Wisconsin and on the Apostle Islands in Lake Superior. The bass Island Sandstone is one example. the sandstone of choice in this group is mostly a red feldspathic (has feldspar as a dominant mineral) sandstone deposited as the final stage of the infilling if the Keweenaw Rift. It is presently considered to be the last Precambrian event in Wisconsin which makes it about 1040 million years old.
This reddish sandstone looks similar to the popular “brownstone” used in many east coast row-houses, churches and government buildings, which made it popular as a building stone in the Midwest. It is not always the hardest or well-cemented rock, so it is susceptible to weathering. This is evident on the Milwaukee Club and the Button Block building in Milwaukee’s downtown area, where the sidewalk is sometime a little red from the decaying stone, and small pieces have fallen to the street.
Mankato-Kasota Limestone: This sedimentary rock is part of the Oneota Dolostone Formation of southern Minnesota. It is quarried near the town of Mankato, Minnesota. The age of this rock is ~ 450-500 m.y. which places it in the lower Ordovician Period. The rock is a very fine-grained yellowish-tan dolostone consisting almost entirely of dolomite. The high dolomite content means that, for a sedimentary rock, it is relatively resistant to weathering and is therefore widely used as a building stone. The Oneota dolostone was laid down in a shallow embayment of an ancient Ordovician sea. It contains relatively few fossils and for this reason it has been suggested that this embayment was hypersaline and could not support a wide range of life forms.
Morton Gneiss (Rainbow Granite): This metamorphic rock is a migmatitic gneiss of Archaean age (about 3600 m.y.). This means that it is one of the oldest rocks that have ever been dated and is certainly the oldest rock in wide use as a decorative building material. It is quarried near the town of Morton , Minnesota. The primary minerals present in this rock are quartz, potassium feldspar (microcline),plagioclase feldspar and biotite. At one time this rock was very close to melting and the swirly, contorted banding that is so evident is due to plastic deformation near the melting point of the rock.
Rockville White: This coarse grained igneous rock is a true granite of Early Proterozoic age (~1730 m.y.). It is quarried near the town of Rockville, Minnesota. The main minerals evident in the rock are quartz, potassium feldspar (microcline), plagioclase feldspar, and biotite. Smaller amounts of zircon, apatite, hornblende, chlorite, sericite and sphene also occur. The texture is porphyritic with large crystals of potassium feldspars (“phenocrysts”) set in an otherwise equi-granular matrix. The rock is very chemically and petrologically very similar to Diamond Pink. The main difference is the absence of pink color in the feldspars.
Wauwatosa Limestone: This dolomitic rock is most frequently referred to as limestone, in spite of its composition of calcium and magnesium carbonate. It is also known as Niagarian Dolomite, because it is the same rock unit that caps Niagara Falls in Western New York. It is used throughout eastern Wisconsin for buildings and roadwork because it is close to the surface and easy to quarry. It forms the prominent ridge that runs form Door County through Milwaukee and Waukesha and continues just below the surface though Racine and Chicago. It is middle Silurian age (450 million years old) and noted for the ancient coral reefs that are found in it. The reef structures provide clues to Wisconsin’s past environment, suggesting that Wisconsin was once part of a shallow tropical ocean. The Milwaukee Public Museum has an exquisite diorama showing life on a Silurian reef. Fossils form quarries in S.E. Wisconsin can be viewed in the Greene Gallery on the UWM campus.
The rock tends to be light tan to gray in color and fairly compact or dense. This makes for an ideal building stone, especially since it is close to home.
Winona Travertine: This sedimentary rock is part of the Oneota Dolostone Formation of southern Minnesota and as such is essentially the same rock as the Mankato-Kasota Limestone
Woodbury Granite: This coarse grained igneous rock is a true granite that is quarried near the town of Woodbury, Vermont. The Vermont granites are much younger than the rest of the granitic rocks seen in this field trip. The age of this rock is ~300 m.y. which places it in the Mississippian Period (mid Paleozoic Era). It is very similar to the Bethel White quartz monzonite, but with a little more silica content.