Slate shingles cover the central dome and roof of the National Museum
of Natural History. Slate makes good shingles because it splits easily
into thin, durable sheets of solid rock. Why? It contains platelike
mica minerals arranged in narrowly spaced layers. Several varieties
of granitea durable and beautiful igneous rockface and
trim the Museum. A bright green-and-orange granite, unakite, accents
the Mall-side stairs. The green is the mineral epidote, and the
orange comes from hematite inclusions in orthoclase.