💎 Rock cycle and minerals

The rock cycle describes how rock is never really finished changing, it constantly transforms from one type into another over long stretches of time, driven by heat, pressure, and weathering. Rock can melt underground and cool into new rock, get squeezed and heated without fully melting, or wear down into tiny pieces that eventually pack back together into something new. There is no true starting point in the cycle, any single rock could be partway through any stage at any moment, and the whole process simply keeps looping around and around.

Igneous rock forms when melted rock cools and hardens, either quickly at the surface after a volcanic eruption or slowly underground, which affects how big its mineral crystals grow. Sedimentary rock forms when tiny bits of sand, mud, or shell settle in layers, usually underwater, and get pressed together over time until they harden into solid rock. Metamorphic rock starts as one of the other two types, but gets squeezed and heated so intensely underground, without fully melting, that it transforms into something new, often with wavy, streaked patterns inside.

A mineral is a single, pure natural substance with its own specific chemical makeup and crystal structure, like quartz or salt, while a rock is usually a mixture of several different minerals packed together. Think of minerals as ingredients and rock as the finished dish, the same handful of common minerals can combine in different ratios to create many completely different kinds of rock. Scientists identify minerals by testing specific clues, like how hard they are, what color they leave when scratched against a rough surface, and how their crystals are shaped.

Crystals form when atoms of a mineral arrange themselves into a repeating, orderly pattern, and the slower and more undisturbed that process happens, the bigger and more perfect the resulting crystal usually grows. Some crystals form from melted rock cooling extremely slowly deep underground, giving atoms plenty of time to line up neatly, while others form from mineral-rich water slowly filling a crack or hollow space in rock. A gem is simply a mineral crystal considered rare, beautiful, or durable enough to be cut, polished, and worn as jewelry, even though chemically it may not be so different from an ordinary rock-forming mineral.