1. Igneous Rocks: These rocks are formed from the cooling and solidification of magma (molten rock) or lava.
* Intrusive igneous rocks: These form when magma cools and solidifies beneath the Earth's surface (examples: granite, gabbro).
* Extrusive igneous rocks: These form when lava erupts onto the Earth's surface and cools (examples: basalt, rhyolite).
2. Sedimentary Rocks: These rocks are formed from the accumulation and cementation of sediments, which are fragments of other rocks, minerals, or organic matter.
* Clastic sedimentary rocks: These are made from fragments of other rocks (examples: sandstone, shale, conglomerate).
* Chemical sedimentary rocks: These are formed from the precipitation of minerals from water (examples: limestone, rock salt, gypsum).
* Organic sedimentary rocks: These are formed from the accumulation of organic matter, like the remains of plants and animals (examples: coal, oil shale).
3. Metamorphic Rocks: These rocks are formed when existing igneous, sedimentary, or even other metamorphic rocks are subjected to intense heat and pressure. This causes changes in their mineral composition, texture, and structure.
* Foliated metamorphic rocks: These have a layered or banded appearance (examples: slate, schist, gneiss).
* Non-foliated metamorphic rocks: These do not have a layered appearance (examples: marble, quartzite).
In addition to these major rock types, the crust also contains:
* Minerals: These are naturally occurring, inorganic solids with a definite chemical composition and crystalline structure. They are the building blocks of rocks.
* Soil: This is a mixture of weathered rock fragments, organic matter, water, and air. It is formed through the breakdown of rocks and the accumulation of organic material.
* Water: Water is found in the crust in various forms, including groundwater, rivers, lakes, and oceans.
* Air: Air pockets can be trapped within the spaces between rock fragments and soil particles.
The composition of the Earth's crust varies depending on the location. For example, the oceanic crust is primarily composed of basalt, while the continental crust is more diverse and includes a wider range of rock types, including granite, sandstone, and limestone.
