Nature · Earth Science
The stone archive of Earth’s history
A rock is a naturally occurring solid made of one or more minerals. Every rock on Earth belongs to one of three great families — igneous, sedimentary or metamorphic — and all are endlessly recycled through the rock cycle, a slow dance of melting, weathering, burial and heat spanning billions of years.
Rocks form in three fundamental ways: by cooling from molten magma (igneous), by the compaction of layered sediments (sedimentary), or by the transformation of existing rock under intense heat and pressure (metamorphic). The rock cycle links all three — any rock can, in time, become any other.
Sedimentary layers, an igneous intrusion cooling from a magma chamber, and metamorphic rock forged where heat meets the surrounding strata.
Born of fire and cooling magma
When molten rock cools it crystallises into igneous rock. Slow cooling deep underground grows large crystals (granite); rapid cooling at the surface makes fine or glassy rock (basalt, obsidian).
Pressed page by page from ancient debris
Weathered fragments, shells and chemical deposits settle in layers and are cemented together over time. Their neat strata are Earth’s history book — and the only rocks that preserve fossils.
Transformed by heat and crushing pressure
Deep burial or tectonic squeezing changes rock without melting it, re-growing its minerals into new forms. Limestone becomes marble; shale becomes slate then schist and gneiss.