Gypsum
Endeavour Crater, Meridiani Planum, Terra Meridiani, Mars
A photo by NASA's Mars rover Opportunity of a gypsum vein* (formerly thought to be anhydrite), 1 - 2 cm wide and 40 - 50 cm long. The rover's Alpha Particle X-ray Spectrometer identified plentiful calcium and sulfur. Image Credit: NASA/JPL-Caltech/Cornell/ASU.
*Ref.: Farrand, W.H., Johnson, J.R., Rice, M.S., Wang, A., Bell III, J.F. (2016): ...