NASA's Curiosity rover uncovers 'mind-blowing' yellow sulfur crystals on Mars

[eppur_se_muova]

7. Clarification: ELEMENTAL sulfur is low-melting and volatile; it can be both melted and volatilized by steam.

Sulfur is well-known to sublime readily on heating. This is why finding elemental sulfur is so surprising -- unless it was recently deposited, surface deposits of sulfur should have had time to sublime away, even at the low temps of the Martian surface.

These crystals were found inside a rock; modeling how fast sulfur vapor could have diffused through the rock could give a (very rough) estimate of how old it was. An age of thousands of years might be reasonable; I doubt one of millions of years would be. So this could be a potential clue to Mars' (relatively) recent past.