On July 4, 1997, the Amptek XR-100 X-Ray Detector landed on Mars. For its unique design and reliability, this detector was selected for the Pathfinder Mission and placed on the Sojourner arm to perform rock and soil analysis using x-ray fluorescence techniques.
The Alpha Proton X-Ray Spectrometer (APXS) onboard the Mars Pathfinder micro-rover is designed to provide a complete detailed chemical analysis of Martian soil and rocks. The Amptek XR-100T X-Ray Detector with the A250 Charge Sensitive Preamplifier provides the APXS with x-ray fluorescence capability.
Here is the first rock spectrum from Mars!
Courtesy of the University of Chicago.