The very tip of the Washington Monument is topped with a small, 100-ounce (about 2.8 kg) pyramid made of solid aluminum. At the time of its completion in December 1884, aluminum was considered a precious and rare metal, comparable in price to silver, because the modern industrial process for refining it (the Hall-Héroult process) had not yet been discovered. The U.S. government chose aluminum for the pyramid—known as the capstone or apex—because of its durability, its non-staining properties, and its ability to conduct electricity, serving as a primary component of the monument's original lightning protection system. The pyramid is roughly 8.9 inches tall and features inscriptions on its four sides, including the Latin phrase "Laus Deo" (Praise be to God) on the east-facing side. Over the decades, the aluminum has been struck by lightning hundreds of times, resulting in slight "pitting" and melting at the very point, which was addressed during various restoration projects. Today, the tip is protected by a series of copper lightning rods, but the original 19th-century aluminum pyramid remains in place as a historical and engineering marvel of the era.