1. Origin: How the rock was formed. This leads to the three main categories:

* Igneous rocks: Formed from the cooling and solidification of magma or lava.

* Sedimentary rocks: Formed from the accumulation and cementation of sediments.

* Metamorphic rocks: Formed when existing rocks are transformed by heat, pressure, or chemical reactions.

2. Mineral composition: The specific minerals that make up the rock. This can vary greatly depending on the rock's origin and the conditions under which it formed.

3. Texture: The overall appearance and arrangement of the rock's mineral grains. This includes factors like grain size, shape, and how the grains are arranged.

These three characteristics work together to provide a complete picture of a rock's history and formation.