Rock Cycle and Types of Rocks

The rock cycle is a fundamental concept in geology that explains the continuous transformation of rocks over millions of years. This process involves the formation, breakdown, and reformation of three main types of rocks: igneous, sedimentary, and metamorphic.

Igneous Rocks

Igneous rocks form when hot molten rock solidifies, either below the Earth's surface or after volcanic eruptions. These rocks are very common in the Earth's crust.

Example: Granite and basalt are common igneous rocks. Granite can become very old, while basalt is the most common volcanic rock.

Sedimentary Rocks

Sedimentary rocks are formed from eroded pieces of other rocks and the remains of plants and animals. These fragments accumulate in low areas and are compressed into new rocks.

Highlight: Fossils are often found in sedimentary rocks, which can be seen in layers called strata.

Example: Sandstone is formed from mud and sand, while limestone is made from seashells, diatoms, and calcium-filled water.

Metamorphic Rocks

Metamorphic rocks are created from existing sedimentary or igneous rocks that are transformed by heat, pressure, or the intrusion of fluids.

Example: Marble is metamorphosed limestone, quartzite is metamorphosed sandstone, and gneiss sometimes begins as granite.

Vocabulary: Subduction - When tectonic forces draw rocks deep beneath the Earth's surface, contributing to metamorphic rock formation.

The rock cycle diagram illustrates how these rock types can morph back into each other through various geological processes, including weathering, erosion, melting, and compaction.