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  September 4, 2000

Earthly Matters
From Mud to Bricks:
Firing Produces Colorful Transformation

The palette of colors on UConn's main campus is dominated by earthy tones. Green is most widespread, at least when the trees are lush and fragrant. Grays are also common: light tones for granite curbing and sidewalk cement; dark tones for asphalt roads and pathways. White, the color of clouds, is also used for trim.

But the most important and evocative color on campus is that of brick. So familiar is the color of brick - a dusky brownish red - that no other word is needed to describe it.

Bricks are colored by neither paint nor pigment. Instead, this hue is produced incidentally by the chemical transformation of iron-bearing minerals when the raw material is being "fired." Sometimes, while strolling through campus, I try to imagine how it would look if the bricks had never been oven-baked. New buildings would be battleship gray, which is the raw color of mineral-rich mud. Old buildings would have long since softened back into mud and washed away in the rain, leaving behind their skeletons of structural steel.

Each of our bricks has a similar story - one beginning with the tough, ancient rocks of New England, passing through several ice-age transformations, and ending in a factory kiln.

To begin, most of New England's rocks contain trace quantities of dark crystals - pyroxene, amphibole, garnet, or magnetite - containing iron in its "reduced," or un-oxidized state. Along with the more familiar light-colored minerals, these dark minerals were physically crushed and abraded into powder by the great Laurentide Ice Sheet, which passed over New England between 15,000 and 25,000 years ago.

Chemically unaltered, this battleship-gray glacial "flour" was washed outward from the ice by turbid meltwater streams, where it accumulated in broad glacial lakes, the largest of which - Glacial Lake Hitchcock - lay over the Connecticut River Valley near Hartford. Layer after layer of silty clay accumulated in an environment deficient in oxygen, preventing the mud from "rusting" into the familiar yellowish brown colors of local soils.

Brick makers of any era, after stripping away the forest, topsoil, and sand overburden, have obtained the raw material for bricks by merely gouging out the unweathered mud. They strengthen it with temper, pack it into molds, dry it completely, then bake it at very high temperatures in a kiln.

As it is fired, the constituent minerals partially recrystallize, converting the cold lake-bottom mud into a hot artificial rock called brick. In the process, microscopic fragments of iron-bearing minerals turn color from drab shades of green and gray to a brighter shade of earthy red, a color that is exceptionally stable in our oxygenated atmosphere.

I am glad for this incidental transformation of color. The red stain of oxidation conveys a sense of belonging and durability. UConn's buildings, raised up from icy lake bottoms, will stand for centuries.

Robert Thorson

Earthly Matters, a series on the geology of the University's campuses, is contributed by Robert Thorson, a professor of geology.