Keystone (limestone)
File:The Florida Keys Memorial, view of monument 4856.jpg
Keystone is a type of limestone, or coral rag, quarried in the Florida Keys, in particular from Windley Key fossil quarry, which is now a State Park of Florida. The limestone is Pleistocene in age, and the rock primarily consists of scleractinian coral, such as Elkhorn coral and Brain coral.
Image:Fossil_Reef_Windley_Key_1.jpg (Diploria) at the quarry. US Quarter near top for scale.]]
The Hurricane Monument, commemorating victims of the Labor Day Hurricane of 1935, and located at mile marker 82 on U.S. Route 1 near Islamorada, is constructed of keystone, as is the David W. Dyer Federal Building and United States Courthouse.