1. Igneous Rocks:

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

* Types:

* Intrusive Igneous Rocks: Formed when magma cools slowly beneath the Earth's surface, resulting in large crystals (e.g., granite, gabbro).

* Extrusive Igneous Rocks: Formed when lava cools quickly on the Earth's surface, resulting in small crystals (e.g., basalt, rhyolite).

2. Sedimentary Rocks:

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

* Types:

* Clastic Sedimentary Rocks: Formed from fragments of other rocks (e.g., sandstone, shale, conglomerate).

* Chemical Sedimentary Rocks: Formed from the precipitation of minerals from water solutions (e.g., limestone, rock salt, gypsum).

* Organic Sedimentary Rocks: Formed from the accumulation of organic matter (e.g., coal, oil shale).

3. Metamorphic Rocks:

* Formation: Formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

* Types:

* Foliated Metamorphic Rocks: Rocks with a layered or banded appearance due to pressure (e.g., slate, schist, gneiss).

* Non-foliated Metamorphic Rocks: Rocks without a layered appearance (e.g., marble, quartzite).

Further Classification:

Within each group, rocks can be further classified based on:

* Mineral Composition: The types and proportions of minerals present.

* Texture: The size, shape, and arrangement of mineral grains.

* Color: The overall color of the rock.

* Other Properties: Hardness, density, and chemical properties.

Note: This is a simplified overview of rock classification. There are many other factors and nuances that are considered by geologists when classifying rocks.