1. Igneous Rocks:

* Formation: Formed from the cooling and solidification of molten rock (magma or lava).

* Classification: Based on their mineral composition, texture (size and arrangement of crystals), and cooling history.

* Examples: Granite, basalt, obsidian, pumice

2. Sedimentary Rocks:

* Formation: Formed from the accumulation, compaction, and cementation of sediments (fragments of other rocks, minerals, or organic matter).

* Classification: Based on the type of sediment (clastic, chemical, or organic), grain size, and layering.

* Examples: Sandstone, limestone, shale, coal

3. Metamorphic Rocks:

* Formation: Formed from the transformation of existing rocks (igneous, sedimentary, or even other metamorphic rocks) due to heat, pressure, or chemical reactions within the Earth's crust.

* Classification: Based on the original rock (protolith) and the intensity and type of metamorphism.

* Examples: Marble, slate, gneiss, schist

In summary, the key to classifying rocks is to understand their origin:

* Igneous: Cooling and solidification of molten rock

* Sedimentary: Compaction and cementation of sediments

* Metamorphic: Transformation of existing rocks under heat, pressure, or chemical reactions

Let me know if you would like more details on any of these rock types!