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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.
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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
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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 buffcolored 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.
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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 magma that 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.