Gadolinium is silvery white and has a metallic luster. It is relatively stable in dry air, but in moist air it quickly forms a coating of oxidation which spalls off. Gadolinium has an extremely high thermal neutron capture cross-section, but its fast burn out rate limits its effectiveness as a nuclear control rod material. Because it is strongly paramagnetic, solutions containing Gadolinium are often used as intravenous radioactive contrast agents. It is also found in nuclear marine propulsion systems, compact discs and computer memory.