The mineral is nearly opaque and appears dark red-brown in thin crystals.[7] The analyzed samples contain less than 10% impurities (Y, Al, Mn, Cr, Nb and other rare-earth element) and up to 0.01% (100 ppm) of uranium.[25] Presence of a significant amount of uranium allowed scientists to estimate the age of tranquillityite and some associated minerals in Apollo 11 samples as 3710 million years using the uranium–lead dating technique.[20]