QUESTION:
Do the rocks on Mars contain calcium carbonate or gypsum?

ANSWER from Jack Farmer on May 13, 1999:
Elemental analyses were acquired for soils at both of the Viking lander sites
and more recently, for rocks and soils at the Pathfinder landing site.
Unfortunately, with only elemental abundance data to go on, it is hard to say
how those elements are arranged into minerals. However, the presence of
duracrust-like soils at all three landing sites, as well as enrichment in
sulfur suggests that sulfates, such as gypsum may be present. The evidence for
carbonates is less compelling, although we do know from studies of some
martian meteorites (e.g. the so-called Alan Hills (ALH 84001) meteorite
discovered in Antarctica) that carbonates are also occur as fracture-fills in
some rocks. - Jack Farmer