A "Chicago in Stone and Clay" Companion, Part AV-A: Egypt in the Windy City | Avondale Center (1980)
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: 8.8; pp. 124-126.
A close-up of the eastern elevation.
One of the most historically significant building stones in Chicago and indeed in the whole world is this one. It's the Aswan Granite, quarried in eastern Egypt for fifty centuries.
Geologists refer to this sort of granite as an A-type. As such, it belongs to a group of granitoids thought to form not in a regime of subduction or compressional tectonics, but rather in extensional settings—mantle plumes or continental stretching and rifting caused by the process known as slab rollback.
Mineralogically speaking, the Aswan Granite is a striking blend of pink to brick-red potassium feldspars, glassy-gray quartz, and black biotite mica. However, plagioclase feldspar, always in short supply in A-type granitoids, is predictably lacking here.
For considerably more on this site, 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 AV-A: Egypt in the Windy City | Avondale Center (1980)
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: 8.8; pp. 124-126.
A close-up of the eastern elevation.
One of the most historically significant building stones in Chicago and indeed in the whole world is this one. It's the Aswan Granite, quarried in eastern Egypt for fifty centuries.
Geologists refer to this sort of granite as an A-type. As such, it belongs to a group of granitoids thought to form not in a regime of subduction or compressional tectonics, but rather in extensional settings—mantle plumes or continental stretching and rifting caused by the process known as slab rollback.
Mineralogically speaking, the Aswan Granite is a striking blend of pink to brick-red potassium feldspars, glassy-gray quartz, and black biotite mica. However, plagioclase feldspar, always in short supply in A-type granitoids, is predictably lacking here.
For considerably more on this site, 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.