Fe-oxide mineral (Fe2O3) that may be the major cause of the red color on Mars. Coarser-grained gray hematite has the same chemical formula as the red variety, but a different crystalline structure. Deposits of gray hematite found in the Terra Meridiani region of Mars may suggest that water once circulated through the region’s rock layers.

Hematite is a common terrestrial mineral often mistaken as a meteorite.

Some or all content above used with permission from J. H. Wittke.