This graph shows the chemical composition of the rock at Gusev Crater dubbed "Mazatzal" after it was brushed and ground by the Mars Exploration Rover Spirit's rock abrasion tool. The data, taken by the rover's alpha particle X-ray spectrometer over the last few sols, show that the amount of chlorine and sulfur tri-oxide in Mazatzal first increased after brushing, then diminished after grinding. The interior of the rock appears to have the same chemical make-up as other volcanic or basalt rocks studied in the Gusev Crater area ("Adirondack" and "Humphrey"). Its outer coating or rind, on the other hand, appears to be of a different constitution.Scientists are still puzzling out the implications of these data.

The larger symbols on the graph represent inferred rock compositions, while the smaller symbols are actual data points. Observations were made at the target dubbed "New York" on Mazatzal.