Like all Americans, we at Lovett Keshet Studio are pondering the same important question:
What is that stunning dark veined marble in the Senate Chamber?
The Senate desk, or rostrum, as it is properly called, is made of a marble called Rosso Levanto, meaning "red from the Levant". While the rostrum can look black or dark purple on CSPAN, the marble ranges from a warm red to this very dark variety. The red colorization of the stone comes from the presence of iron oxides. Some, (nerds like us) might argue this is more of a Serpentine rock - an ophicalcite - than a true marble, but for all practical purposes, it should be used and treated like a marble (not a granite).
Originally, in the 1851 Thomas U. Walter design of the Senate, the rostrum was made of a carved walnut, with symbols and iconography prominently displayed. In 1949 it was replaced as part of a much larger renovation of the room. The renovation solved some structural, acoustical, and ventilation problems with the aging room, but also strove to rid it of its mid-1800's design aesthetic and project the "modern" design taste of the post-war era. See below for before-and-after shots.
The Senate chamber isn't the only hall of power this marble appears in. Both Louis XV and Louis XVI used it for fireplaces within the Versailles Palace. It appears often in religious and government buildings in Italy.
Rosso Levanto is a brecciated, polychrome ornamental stone. It is easy to work and polish, making it popular even in ancient times. Etruscan funerary artifacts have even been found carved from this stone. Because of its softness, the stone is primarily found on interiors.
Historically, Rosso Levanto was quarried from the Liguria region in Italy. The Liguria region of stone is not as well known as Carrara or Verona, however it has been extracting marbles and slate since at least the 12th century. Due to the fragility of some of these environments, few Italian quarries of this Rosso Levanto are still in operation, concentrated around the town of Bonassola in the Ligurian Apennines (SE of Genoa).
Italian quarries still operating are focused less on volume and more on extracting high quality stones that are traditional to Italian architecture and history. Above are images of quarries in the hills of Bonassola, overlooking the Ligurian Sea. Rosso Verde (the green variety) is also quarried here, but only by request.
Today most supply comes out of Turkey and sometimes Greece. The Turkish variety is properly called Rosso Lepanto though the terms are typically used synonymously in the natural stone industry. Above images from Turkish quarries.