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Granite Wall at the FDR Memorial

Geology of Washington, DC

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The Franklin D. Roosevelt Memorial is a sprawling installation made of extremely old reddish-brown granite from South Dakota. (more below)
A stone of rugged drama
Photo (c) 2008 Andrew Alden, licensed to About.com (fair use policy)
Click the photo to see the full-size version. This wall, decorated with bronze panels, is just one element of a large complex of walls, water features, bronzes and inscriptions honoring FDR. The remarkable memorial consists almost entirely of "Carnelian Granite," a commercial name for rock of the Milbank Granite of Early Proterozoic age (approx 2600 million years) quarried in Milbank, South Dakota, by the Cold Spring Granite company. Large amounts were cut and polished for the walkways and steps, but the most important part was furnished in large blocks hand-cut with a rugged surface. The memorial was designed with an unusual degree of attention to the stone by its designer, Lawrence Halprin. A compelling Washington Post article about the stone work and workers was read into the Congressional Record.

The Milbank Granite was described in 1947 as consisting of "approximately 60% dark red feldspar belonging to the orthoclase group, 25% clear quartz and 15% biotite mica." That would make it an alkali-feldspar granite on the QAP classification diagram. A 1995 description of the Carnelian Granite, though, is "reddish brown, coarse-grained porphyritic rock consisting of subequal proportions of quartz, alkali feldspar, and biotite, with minor amounts of plagioclase and opaque minerals." This describes a darker rock than the bulk of the Milbank Granite.

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