Limonite is not a specific mineral, but rather a mineraloid. It's a hydrated iron oxide that is usually a mixture of several different iron oxides and hydroxides, such as goethite, hematite, and lepidocrocite.

While often referred to as "iron ore," it's important to note that limonite is not a pure iron oxide, and therefore not a single mineral. It's a mixture of different iron compounds, making it a mineraloid rather than a mineral.

Here's a breakdown:

* Mineral: A naturally occurring solid with a defined chemical composition and a specific crystal structure.

* Mineraloid: A naturally occurring solid that lacks a defined chemical composition or crystal structure.

So, while limonite is a valuable source of iron, it's classified as a mineraloid due to its variable composition and lack of a defined crystal structure.