Limestone is not a single mineral. It's a rock, composed primarily of the mineral calcite.

Here's why:

* Minerals have a specific chemical composition and crystal structure. Calcite (CaCO₃) is a mineral, but limestone is a rock that can contain other minerals like dolomite, quartz, and clay.

* Rocks are aggregates of one or more minerals. Limestone is an aggregate of calcite (and sometimes other minerals).

* Rocks can have different textures and compositions. Limestone can be formed in various ways, leading to different textures (like crystalline, granular, or fossiliferous) and compositions (including different amounts of calcite and other minerals).

So, while limestone is mainly made of calcite, it's a rock because it's a combination of minerals and can have varying compositions and textures.