Smithsonian Institution Headquarters
Geology of Washington, DC
"The Castle" was built of local sandstone, ideal in all respects except for an unfortunate color change. (more below)
Click the photo to see the full-size version. Sandstone of Triassic age was quarried at Seneca Creek, Maryland, just up the Potomac River to make this handsome building. Triassic sandstones in the Appalachian chain are generally red, but when the building was finished in 1855 it was described as being lilac gray in color. Seneca sandstone was popular, coming out of the quarry fairly soft and hardening after a few years of exposure.
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But as the decades went by the stone turned more and more red, as if it were sunburned, and today the building is much darker than the designer anticipated. As Clark Kimberling puts it, "No one living has seen the Castle in its original color."
Correspondence about the Smithsonian's building includes this description of the Seneca sandstone by geologist David Dale Owen: "When first removed from the parent bed, it is comparatively soft, working freely before the chisel and hammer, and can even be cut with a knife; by exposure, it gradually indurates, and ultimately acquires a toughness and consistency that not only enables it to resist atmospheric vicissitudes, but even the most severe mechanical wear and tear. . . . The singular property which the best quality of these freestones possesses, of hardening by exposure, is one of its most valuable characteristics; permitting it to be wrought at less expense than marble, and imparting to it a durability which increases with age."
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