Folwell - 1
FOLWELL HALL
Folwell Hall was built in 1906-07 to replace Old Main, which had been destroyed in a 1904 fire. Constructed during Cyrus Northrup's term as the university's second president, the building was originally designated as Northrup Hall, but a storm of protest from students, alumni, newspapers and the public led to it being renamed Folwell Hall, after the University's first president, William W. Folwell.
INSIDE
Slabs of beautiful Italian marble line Folwell’s first floor. The marble's cost almost led the Regents to reject the hall's original design, but fortunately the building was completed as planned.
Firewalls were later added as a safety measure, but mirrors installed above the firewalls try to evoke the hall's original expansive nature.
WALLS
Three shades of Italian marble cover the first floor walls.
2ND
Pure marbles are usually white, but small traces of impurities may give marble many hues. Groundwater also moved through the rock along a network of fractures, further altering its color scheme and imbuing the rock with a decorative pattern.
3RD
All three marbles, buff, white and green, originally formed as carbonate mud, deposited on shallow sea floors. Later, the seafloor mud was deeply buried and metamorphosed into marble. Unlike Folwell’s exterior rock, these marbles did not form along an active plate margin, but on marine shelves in a plate interior. As none of the marbles contain any detrital material, they must have formed in areas that were far removed from river outlets or lowland hills. Small fossils are scattered through some of the white marble slabs, attesting to the rock's original marine setting.
LABELS
As seen in Folwell, marble can even occur in shades of green. At first glance, green marble might be confused with serpentine, a green metamorphic rock used to trim Folwell’s floors. However, the two rocks have very different textures. Formed from carbonate sediments, marble has a more mottled or layered texture than serpentine. Hints of the marble's original depositional fabric may remain, such as grain shapes, fossils or and the tracks of burrowing organisms. Serpentine also tends to be a darker shade of green, cut be a complex pattern of white seams or fractures.
FLOORS
Gray limestone covers most of Folwell’s floor surface. Thin rectangular outlines of green serpentine, along with circles and diamonds of white marble, form decorative patterns in the gray limestone.
2ND
All of these rocks have marine origins. The gray limestone and white marble formed as alterations of carbonate mud originally deposited on the bottom of long vanished seas. In contrast, the serpentine formed from the metamorphism of seafloor igneous rock, as plate motion subducted an ancient ocean basin.
LABELS
Although the limestone and marble rocks both originated from marine carbonate mud, their textures now are quite different as a result of their post-depositional history. The mud from which the gray limestone formed, was only buried to a moderate depth, and the mud compacted and recrystallized slightly to create limestone. If this rock had been buried much deeper, it may have been more fully metamorphosed into marble. During metamorphism, much of the depositional fabric is lost, so the white marble looks more homogenous than the gray limestone.
Serpentine is the most completely altered rock present. It formed from the alteration of black igneous seafloor rock (basalt), as a sliver of ocean crust was caught between two converging plates. Tremendous heat and stress altered the rock's texture and mineral composition, creating a dark green rock.
3RD
Thin irregular black seams cut across the slabs of gray limestone., which also contains scattered small fossils. These seams are called stylolites.
LABELS
During burial, pressure causes some of the limestone’s calcite to dissolve. Insoluble impurities present in the calcite crystals were left behind as the calcite dissolved. These impurities were concentrated along the dissolution front. So the dark lines seen in the rock are actually the edges of thin planes of insoluble material left behind as part of the rock dissolved.
Since the stylolite plane forms perpendicular to the direction of maximum stress, geologists can use stylolites’ orientation to determine the direction of the stresses that produced them. This limestone are simply buried, so the only stress on the rock is the weight of overlying rock layers and horizontal stylolites formed. In tectonically active areas though, stress may be applied from many directions. Convergent plate motion can even form vertical stylolites.
FIREWALLS
Two varieties of marble cover the firewalls, separated from one another by a thin border of green serpentine. As relatively recent additions to the building, the firewalls are not composed of exactly the same stone as the hall walls.
LABELS
The white and buff marbles were chosen to match the hall’s original stone, but the buff-colored marble within the serpentine border has a distinctive algal texture not found in the hall’s larger marble panels.
2ND
A complex pattern of color and texture formed as a result of algae coating the irregular surface of an ancient rocky coastline. Algal layers, which formed in shallow sunlit water, were preserved as irregular laminations that coat the upper side of the buff colored rock surface.
LABELS
Crystals of white calcite filled most of the remaining space between the algal-coated rocks, before a darker green mud filled the last of the rock’s open spaces.
OUTSIDE
The lower part of Folwell Hall’s exterior is encased in granite. Granite is an igneous rock that formed as magma slowly cooled and crystallized. Since the rock's crystals are large enough to be seen the magma had to have cooled very slowly, most likely far below the Earth’s surface. Folwell’s granite walls are thought to have originally formed as the roots of an ancient mountain chain that stretched across what is now rolling Minnesota prairie and woodland. These mountains formed as micro-continents collided to build North America.
COLUMN
The granite of the south entrance’s columns and walls formed as magma cooled far beneath the Earth’s surface as the root of an ancient mountain range. As the overlying mountain slowly eroded, the roots rose until they are now exposed as part of Minnesota's landscape.
2ND
The granite used to construct Folwell Hall’s lower wall contains fragments of an even older rock. These fragments broke off and were carried along by the magmathat later cooled to form the granite.
LABELS
Fragments like these are collectively known as xenoliths (Greek for ‘strange rocks’ or ‘foreign rocks’).
WALLS
Although the granite initially appears to be fairly homogenous, on closer examination it contains fragments of older rock known as xenoliths.
2ND
These xenoliths (Greek for 'strange rocks' or ‘foreign rocks’) formed as blocks of older dark gray rock broke off and were carried along by magma (molten rock) as it rose toward the Earth’s surface.
LABELS
Xenoliths are often some of the best clues we have as to the nature of the rocks deep within the Earth. Although some xenoliths come from relatively shallow depths, others are fragments of deep mantle rock.
Although they occur in volcanic systems, natural diamonds are similar in the sense that they only reach the Earth’s surface in fragments of mantle rock caught up in rising magma.