What compound is mainly responsible for Mars's reddish surface color?

What compound is mainly responsible for Mars's reddish surface color? Iron oxide is the main culprit. More precisely, iron(III) oxides—rust-like compounds containing ferric iron—color the fine dust that coats much of the planet.

Mars is not uniformly bright red at ground level. Its surface can look tan, brown, golden, or butterscotch, while dust suspended in the atmosphere and spread across the terrain creates the familiar red-orange appearance seen from space. The redness is largely a thin surface veneer rather than the color of the planet’s entire crust.

The dust contains extremely fine iron-oxide particles, including nanophase ferric oxides. Hematite, a mineral form of iron(III) oxide, is one important example. Mars’s iron likely became oxidized through interactions involving the atmosphere, water or ice, and dust-grinding processes, although the exact pathway remains an area of scientific study.

A common mix-up is copper sulfate, which is blue, or ordinary “rust” as a single mineral. “Iron oxide” is the fair quiz answer; “iron(III) oxide” is the more chemically precise form.