📚 Metamorphic Rocks: Heat, Pressure and Chemical Change | 变质岩：热、压力与化学变化
Metamorphic rocks form when existing rocks are changed by heat, pressure, or chemically active fluids. In KS3 chemistry, this topic links physical conditions with chemical change in solid minerals. It helps explain why the same starting material can produce very different rocks depending on temperature, stress, and time.
变质岩是原有岩石在热、压力或化学活跃流体作用下发生变化而形成的。在 KS3 化学中，这一主题将物理条件与固态矿物中的化学变化联系起来。它有助于解释为什么同一种原始材料会根据温度、应力和时间的不同，生成截然不同的岩石。
1. What Are Metamorphic Rocks? | 什么是变质岩？
A metamorphic rock is an existing rock that has changed its texture, mineral structure, or composition without fully melting. The word 'metamorphic' comes from the Greek words meta (change) and morphe (form). Heat, pressure, and fluids act on the parent rock to produce new crystals while the rock stays essentially solid. This is different from igneous rocks, which cool from molten magma, and sedimentary rocks, which form from compacted fragments.
变质岩是一种已有岩石在未完全熔化的情况下，其结构、矿物构造或成分发生变化的岩石。变质一词来自希腊语的 meta（变化）和 morphe（形态）。热、压力和流体作用于母岩，在岩石基本保持固态的同时生成新的晶体。这与由岩浆冷却形成的火成岩、由碎屑压实形成的沉积岩不同。
2. Protolith: The Parent Rock | 原岩：母岩
The starting rock is called the protolith. For example, shale is a fine-grained sedimentary rock and the protolith of slate. Limestone is the protolith of marble. Granite can be the protolith of gneiss. The protolith's minerals provide the chemical ingredients for new metamorphic minerals. Even a metamorphic rock can become the protolith for a later metamorphic event, so rocks can record several changes over geological time.
最初的岩石称为原岩。例如，页岩是一种细粒沉积岩，是板岩的原岩。石灰岩是大理岩的原岩。花岗岩可以是片麻岩的原岩。原岩中的矿物为新的变质矿物提供了化学成分。即使是一块变质岩，也可以成为后来变质事件的原岩，因此岩石可以记录地质历史上多次变化。
3. Heat and Pressure: The Driving Forces | 热与压力：驱动力
Heat and pressure are the main drivers of metamorphism. Heat speeds up the movement of atoms inside crystals, allowing new crystals to grow without melting. Pressure may be confining pressure from burial or directed pressure from tectonic forces. Directed pressure is especially important because it makes minerals align. The temperature range for most metamorphism is roughly 150 °C to 800 °C. Above this range, rocks may begin to melt and form magma.
热和压力是变质作用的主要驱动力。热量加速晶体内部原子的运动，使新晶体在未熔化的情况下得以生长。压力可以是埋藏产生的围压，也可以是构造力产生的定向压力。定向压力尤其重要，因为它会使矿物发生排列。大多数变质作用的温度范围约为 150 °C 至 800 °C。超过这个范围，岩石可能开始熔化并形成岩浆。
4. Chemical Fluids in Metamorphism | 变质作用中的化学流体
Hot fluids rich in silica, carbonate, or metal ions can move through cracks and pore spaces. These fluids catalyse reactions and help atoms move through the rock. When fluids add or remove elements, the process is called metasomatism. This can create ore minerals such as pyrite or new quartz veins. Water is especially important because it lowers the temperature needed for some minerals to recrystallise.
富含硅、碳酸盐或金属离子的热液可以沿裂缝和孔隙流动。这些流体催化反应，并帮助原子在岩石中移动。当流体带入或带走元素时，该过程称为交代作用。这可以形成黄铁矿等矿石矿物或新的石英脉
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