|There is more information available on this subject at Marble on the English Wikipedia.|
The UNSC uses marble as a building material, for example: the Côte d'Azur Museum of Natural History is constructed mainly of marble. The UNSC also uses marble for various other decorative purposes. When using it as a building material, it is one of the more expensive materials. Iron and steel are two of the lesser expensive materials.
The Covenant also use marble as a decorative material, such as the black marble used to make the San'Shyuum cleric's pestle and mortar. Marble is known for it's hardness, durability, and glossy properties.