The tube of reddish material is engineered regolith to be chemically and mechanically identical to that of planet Mars. Regolith is a mixture of dust, soil, broken rock and other organic materials. It is made with terrestrial materials to match the compositional analysis performed by the Mars rovers.
The main chemical components are 44% silicates, 18% iron oxide, and 13% aluminum oxide. This relatively high iron composition is what gives Mars its reddish color.
NASA uses this material to test their rovers' performance abilities on the planet and to determine how well crops can be grown on Mars.