The very peak of the Washington Monument is not stone, but a 100-ounce solid aluminum pyramid, constructed as part of the monument's lightning protection system. In the 1880s, aluminum was a rare metal, selling for $1.10 per ounce and used primarily for jewelry. The pyramid at the top of the monument was the largest piece of aluminum of its day and was such a novelty that it was displayed at Tiffany's jewelry store before it was placed at the top.