Here's why:

* Abundant: It's the most abundant iron oxide found in the Earth's crust.

* Stable: Hematite is a very stable compound, making it common in various geological formations.

* Widely distributed: It's found in various locations, including sedimentary rocks, metamorphic rocks, and even as a major component of some soils.

While other iron oxides like magnetite (Fe₃O₄) and goethite (FeO(OH)) are also important, hematite holds the title of the most common.