The Rock Cycle
The three main types of rocks—igneous, sedimentary, and metamorphic—are constantly being transformed into one another through a process known as the rock cycle.
1. Igneous Rocks
- Formation: Formed from the cooling and solidification of magma (molten rock) or lava.
- Types:
- Intrusive (Plutonic): Cool and solidify slowly beneath the Earth’s surface, resulting in large crystals (e.g., granite).
- Extrusive (Volcanic): Cool and solidify quickly on or near the Earth’s surface, resulting in small crystals or a glassy texture (e.g., basalt, obsidian).
- Examples: Granite, basalt, pumice, obsidian
2. Sedimentary Rocks
- Formation: Formed from the accumulation and cementation of sediments, which are fragments of other rocks, minerals, or organic matter.
- Types:
- Clastic: Formed from fragments of other rocks (e.g., sandstone, shale, conglomerate).
- Chemical: Formed from the precipitation of minerals from water (e.g., limestone, halite).
- Organic: Formed from the accumulation of organic matter (e.g., coal).
- Examples: Sandstone, limestone, shale, coal
3. Metamorphic Rocks
- Formation: Formed when existing rocks are subjected to extreme heat and pressure, causing them to change in texture and mineral composition.
- Types:
- Foliated: Exhibit a layered or banded appearance due to the alignment of minerals during metamorphism (e.g., gneiss, schist, slate).
- Non-foliated: Do not exhibit a layered appearance (e.g., marble, quartzite).
- Examples: Marble, quartzite, gneiss, schist
The Interconnectedness of the Rock Cycle:
- Igneous rocks can weather and erode into sediments, which can then form sedimentary rocks.
- Both igneous and sedimentary rocks can be subjected to extreme heat and pressure, transforming them into metamorphic rocks.
- Metamorphic rocks can melt and become magma, which can then cool and solidify to form igneous rocks.
This continuous cycle of transformation ensures that the Earth’s crust is constantly evolving and renewing itself.