A "Chicago in Stone and Clay" Companion, Part 4: Massive Majesty | Aon Center (1973)
This series complements my award-winning guidebook, Chicago in Stone and Clay: A Guide to the Windy City's Architectural Geology. Henceforth I'll just call it CSC.
The CSC section and page reference for the building featured here: 5.9; pp. 51-53.
Standing on the southern side of E. Randolph Street and looking northwestward.
Behold the lower half, approximately, of the 83-story Aon Center, formerly known as the Standard Oil Building and the Amoco Building. Completed in 1973, it was originally clad in slabs of Italian Carrara Marble sliced too thin to bear the rigors of Chicago's continental climate.
By the time I took this photo, the Carrara's replacement, Mount Airy Granodiorite, had been doing its job for about a decade. While it is no means as lustrous as the original, its monumental paleness nevertheless conveys the building's "Look on my Works, ye Mighty, and despair!" messaging quite adequately. The spire-topped Two Prudential Plaza snuggling next to it provides a nice contrast, too, with its darker, pinkish-gray Mondariz Granite exterior.
As noted in previous posts, I love the Aon, that great hulking beast, all the more for its problems and its detractors. It's good that we have been able to construct such breathtaking structures before our time to do such things runs out.
Quarried in North Carolina, the Mount Airy has been radiometrically dated to 334 ± 3 Ma ago, which places its origin in the Mississippian subperiod (Lower Carboniferous period). As a granodiorite, it's a granitoid rock whose feldspar content is mostly in the form of plagioclase. True granites, on the other hand, contain a higher proportion of alkali feldspars. Such petrologic distinctions are lost on architects, builders, and quarry operators, however. So they call this rock selection the Mount Airy Granite instead.
As is duly noted in CSC, the Mount Airy Granodiorite can also be found and scrutinized at two other Windy City sites—the Congress Plaza Hotel and Graceland Cemetery's Lehmann Mausoleum.
For much more on the site touched upon here, get and read Chicago in Stone and Clay, described at its Cornell University Press webpage.
The other photos and discussions in this series can be found in my "Chicago in Stone and Clay" Companion album. In addition, you'll find other relevant images and descriptions in my Architectural Geology: Chicago album.
A "Chicago in Stone and Clay" Companion, Part 4: Massive Majesty | Aon Center (1973)
This series complements my award-winning guidebook, Chicago in Stone and Clay: A Guide to the Windy City's Architectural Geology. Henceforth I'll just call it CSC.
The CSC section and page reference for the building featured here: 5.9; pp. 51-53.
Standing on the southern side of E. Randolph Street and looking northwestward.
Behold the lower half, approximately, of the 83-story Aon Center, formerly known as the Standard Oil Building and the Amoco Building. Completed in 1973, it was originally clad in slabs of Italian Carrara Marble sliced too thin to bear the rigors of Chicago's continental climate.
By the time I took this photo, the Carrara's replacement, Mount Airy Granodiorite, had been doing its job for about a decade. While it is no means as lustrous as the original, its monumental paleness nevertheless conveys the building's "Look on my Works, ye Mighty, and despair!" messaging quite adequately. The spire-topped Two Prudential Plaza snuggling next to it provides a nice contrast, too, with its darker, pinkish-gray Mondariz Granite exterior.
As noted in previous posts, I love the Aon, that great hulking beast, all the more for its problems and its detractors. It's good that we have been able to construct such breathtaking structures before our time to do such things runs out.
Quarried in North Carolina, the Mount Airy has been radiometrically dated to 334 ± 3 Ma ago, which places its origin in the Mississippian subperiod (Lower Carboniferous period). As a granodiorite, it's a granitoid rock whose feldspar content is mostly in the form of plagioclase. True granites, on the other hand, contain a higher proportion of alkali feldspars. Such petrologic distinctions are lost on architects, builders, and quarry operators, however. So they call this rock selection the Mount Airy Granite instead.
As is duly noted in CSC, the Mount Airy Granodiorite can also be found and scrutinized at two other Windy City sites—the Congress Plaza Hotel and Graceland Cemetery's Lehmann Mausoleum.
For much more on the site touched upon here, get and read Chicago in Stone and Clay, described at its Cornell University Press webpage.
The other photos and discussions in this series can be found in my "Chicago in Stone and Clay" Companion album. In addition, you'll find other relevant images and descriptions in my Architectural Geology: Chicago album.