Rocks and the rock cycle

In short: Rocks belong to three groups: igneous (from solidified melt), sedimentary (from deposited material) and metamorphic (transformed by pressure and heat). They convert into one another in a cycle.

In more detail: The cycle takes millions of years and is driven by plate tectonics, weathering and erosion.

In detail

• Igneous rocks: Granite (solidified slowly at depth), basalt (quickly at the surface).
• Sedimentary rocks: Sandstone, limestone, claystone. They often contain fossils.
• Metamorphic rocks: Marble (from limestone), gneiss (from granite), slate.
• Weathering and erosion: Wind, water, frost and plants break rock down; rivers carry it away.
• Importance: Rocks provide building materials, ores and raw materials; soil arises from weathered rock (bodenaufbau-und-humus, plattentektonik).