1. By their origin (how they were formed): This is called the igneous, sedimentary, and metamorphic classification.

* Igneous rocks form from the cooling and solidification of magma (molten rock) or lava.

* Sedimentary rocks form from the accumulation and cementation of sediments, like sand, silt, and shells.

* Metamorphic rocks form when existing igneous or sedimentary rocks are transformed by heat, pressure, or chemical reactions.

2. By their mineral composition: This classifies rocks based on the types of minerals they contain. This is a more detailed approach and is often used within each of the three main classifications.

For example, within igneous rocks, you have rocks like granite (which is rich in quartz and feldspar) and basalt (which is rich in pyroxene and olivine). Within sedimentary rocks, you have sandstone (made of quartz grains), limestone (made of calcium carbonate), and shale (made of clay minerals).

So, while the igneous, sedimentary, and metamorphic classification is the most common and fundamental, the mineral composition classification provides a more detailed and specific way to categorize rocks.