Jake Matijevic was found to be high in elements consistent with the mineral feldspar, such as sodium and potassium, and low in elements such as magnesium and iron.
But the science team on Curiosity needed a target to try out the first close-contact work using the rover's arm-held X-ray-spectrometer, APXS. So the dark pyramid was chosen and informally given the name Jake Matijevic in honour of a recently deceased rover engineer.