29/07/2026
THE THREE MAJOR TYPES OF ROCKS
Rocks are naturally occurring solid materials that make up the Earth's crust. They are composed of one or more minerals and are classified according to how they are formed.
1. IGNEOUS ROCKS
Igneous rocks are formed when molten rock (magma beneath the Earth's surface or lava at the surface) cools and solidifies. Their texture depends on the rate of cooling. Slow cooling beneath the Earth's surface produces coarse-grained intrusive (plutonic) rocks with large crystals, while rapid cooling at the surface forms fine-grained extrusive (volcanic) rocks with very small crystals.
Examples: Granite (intrusive) and Basalt (extrusive).
2. SEDIMENTARY ROCKS
Sedimentary rocks are formed through the accumulation, compaction, and cementation of sediments such as rock fragments, minerals, and organic materials. These sediments are transported by water, wind, ice, or gravity before being deposited. Sedimentary rocks often occur in layers and may contain fossils, making them important records of past environments and life on Earth.
Examples: Sandstone and Limestone.
3. METAMORPHIC ROCKS
Metamorphic rocks are produced when pre-existing rocks are transformed by intense heat, pressure, and chemically active fluids without completely melting. This process changes the mineral composition, texture, and structure of the original rock. Metamorphic rocks can originate from igneous, sedimentary, or even older metamorphic rocks.
Examples: Slate and Schist.
IMPORTANCE OF ROCK CLASSIFICATION
The classification of rocks helps geologists interpret Earth's geological history, identify mineral and energy resources, assess engineering properties of rocks, and understand the dynamic processes that continually reshape the planet through the rock cycle.
Understanding rocks is the first step toward understanding the Earth. Every rock tells a story of formation, transformation, and the continuous evolution of our planet.
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