This graphic presents information gained by examining part of the Martian rock called "Tisdale 2" with the alpha particle X-ray spectrometer on Mars rover Opportunity and comparing the composition measured there with compositions of other targets examined by Opportunity and its rover twin, Spirit.

The comparison targets are soil in Gusev crater, examined by Spirit; the relatively fresh basaltic rock Adirondack, examined by Spirit; the stony meteorite Marquette examined by Opportunity; and Gibraltar, an example of sulfate-rich bedrock examined by Opportunity. The target area on Tisdale 2, called "Timmins 1," contains elevated levels of bromine (Br), zinc (Zn), phosphorus (P), sulfur (S) and chlorine (Cl) relative to the non-sulfate-rich comparison rocks, and high levels of zinc and phosphorus relative to Gibraltar.