1. Igneous Rocks: These are formed from the cooling and solidification of magma (molten rock) or lava.
* Intrusive Igneous Rocks: Form when magma cools and solidifies beneath the Earth's surface. They typically have large crystals due to slow cooling. Examples: granite, gabbro.
* Extrusive Igneous Rocks: Form when lava erupts onto the Earth's surface and cools rapidly. They typically have small crystals or are glassy. Examples: basalt, rhyolite.
2. Sedimentary Rocks: These are formed from the accumulation and cementation of sediments, which are fragments of other rocks, mineral grains, or organic matter.
* Clastic Sedimentary Rocks: Formed from fragments of other rocks. Examples: sandstone, shale, conglomerate.
* Chemical Sedimentary Rocks: Formed from the precipitation of minerals from water. Examples: limestone, rock salt, gypsum.
* Organic Sedimentary Rocks: Formed from the accumulation of organic matter. Examples: coal, oil shale.
3. Metamorphic Rocks: These are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemically active fluids.
* Foliated Metamorphic Rocks: Have a layered or banded appearance due to the alignment of minerals under pressure. Examples: slate, schist, gneiss.
* Non-foliated Metamorphic Rocks: Do not have a layered appearance. Examples: marble, quartzite.
How rock types can change:
* Igneous to Sedimentary: Igneous rocks exposed at the surface are weathered and eroded, creating sediments that can be transported and deposited to form sedimentary rocks.
* Sedimentary to Metamorphic: Sedimentary rocks buried deep within the Earth are subjected to heat and pressure, transforming them into metamorphic rocks.
* Metamorphic to Igneous: Metamorphic rocks can be melted by intense heat, forming magma, which then cools and solidifies as igneous rocks.
* Igneous to Metamorphic: Igneous rocks can also be subjected to heat and pressure, transforming them into metamorphic rocks.
The Rock Cycle:
This continuous process of rock transformation is known as the rock cycle. It is a fundamental concept in geology that explains how the different rock types are interconnected and how they evolve over time.
