Hematite on Mars

The Opportunity lander has confirmed the presence of hematite from its infrared color, that is, the spectrum recorded by the rover's thermal emission spectrometer (TES). Look at the global map of hematite on scientist Virginia Hamilton's site for the satellite version of the TES observations. Meridiani Planum is the tiny patch of hematite-like ground near the zero meridian, the only such spot on the planet. Whatever we learn from this exceptional region, we must be cautious in applying to the rest of Mars.

Hematite isn't really much to look at: a dark, metallic mineral. Earth has enormous deposits of it dating from the Archean period when the atmosphere had no oxygen. It makes up the black stripes in this piece of tiger iron in the Rock Gallery.