sentences:  The sand in Olympia Undae is extremely dark in color and probably consists of basaltic rock fragments.The surface of Olympia Undae has a strong TES Type 2 spectral signature, indicating that the surface materials consist of basaltic andesite or weathered basalt and/or basaltic glass.In 2005, the OMEGA instrument on the Mars Express orbiter detected high concentrations of gypsum in the eastern portion of Olympia Undae (centered at 244.5°E, 80.2°N).