Classification of Rocks

Rocks can be classified into three main types based on their origin:

Formation: Igneous rocks form when magma cools and solidifies. They are the first rocks to form from the Earth's mantle and crust.
Intrusive vs. Extrusive:
- Intrusive rocks form when magma cools slowly underground, allowing large crystals to grow (e.g., granite).
- Extrusive rocks form when lava cools quickly on the surface, leading to smaller crystals (e.g., basalt).
Characteristics:
- All igneous rocks are crystalline and massive, lacking layers.
- Crystals form from a mix of elements, like silica, iron, and magnesium.

Formation: Sedimentary rocks form from layers of compressed sediments, which can include fragments of other rocks, organic matter, and minerals.
Types:
- Mechanically formed: Conglomerates and sandstones form from the accumulation of sediments due to erosion by wind, water, and ice.
- Organically formed: Limestone and coal form from biological processes, where remains of marine organisms or plant material accumulate and consolidate.

Formation: Metamorphic rocks are created when existing rocks are subjected to high temperatures and pressures, causing physical and chemical changes.
Characteristics:
- Often have layered structures and can contain new minerals formed from the original rock.
- Examples include gneiss (from granite) and marble (from limestone).

Igneous Rocks: Used for building materials and contain valuable metals such as copper and gold.
Sedimentary Rocks: Cement manufacturers use limestone and shale; clay is used for bricks and tiles.
Metamorphic Rocks: Utilized in construction (e.g., crushed gneiss for roads) and decorative purposes (e.g., slate for tiles).