Answer: hematite

AnswerCrossword Clue
HEMATITEIron ore
HEMATITEMineral found on Mars in 1998 that suggests the former presence of water
HEMATITEMain ore of iron
hematitean ore of iron
hematitevery common mineral, iron oxide, Fe2O3, occurring in steel-gray to black crystals and in red earthy masses: the principal ore of iron