Metamorphic Rocks | 变质岩

📚 Metamorphic Rocks | 变质岩

In KS3 chemistry, a metamorphic rock is a rock that has been changed by heat, pressure, or chemical fluids without melting completely. The original rock, called the parent rock or protolith, keeps its solid state but its minerals, texture, and sometimes its chemical composition are transformed.

在 KS3 化学中，变质岩是指未经完全熔化而被热、压力或化学流体改变的岩石。原始岩石称为母岩或原岩，它保持固态，但其矿物、结构和有时化学成分发生了变化。

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1. What Are Metamorphic Rocks? | 什么是变质岩？

Metamorphic rocks form when existing rocks are changed by heat, pressure, or chemically active fluids. The word ‘metamorphic’ comes from the Greek words ‘meta’ meaning change and ‘morphe’ meaning form.

当原有岩石被热、压力或化学活性流体改变时，就会形成变质岩。’变质岩’ 一词来源于希腊语 ‘meta’（变化）和 ‘morphe’（形态）。

Common examples include marble, slate, schist, and gneiss. They do not form by cooling from magma, nor by piling up and cementing sediment like sedimentary rocks.

常见的例子包括大理岩、板岩、片岩和片麻岩。它们既不是由岩浆冷却形成的，也不像沉积岩那样由沉积物堆积和胶结而成。

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2. Where Metamorphic Rocks Fit in the Rock Cycle | 变质岩在岩石循环中的位置

Metamorphic rocks are one of the three main rock groups, alongside igneous rocks and sedimentary rocks. They are usually created deep inside the Earth’s crust.

变质岩是三大类岩石之一，与火成岩和沉积岩并列。它们通常在地壳深处形成。

• Igneous rocks form from cooling magma or lava. | 火成岩由岩浆或熔岩冷却形成。
• Sedimentary rocks form from compressed and cemented sediments. | 沉积岩由沉积物压实和胶结形成。
• Metamorphic rocks form from pre-existing rocks changed by heat and pressure. | 变质岩由先前存在的岩石受热和压力变化形成。

Any rock type can become a metamorphic rock. Igneous, sedimentary, or even older metamorphic rocks can all be changed into new metamorphic rocks.

任何类型的岩石都可以变成变质岩。火成岩、沉积岩，甚至更古老的变质岩，都可以被改变为新的变质岩。

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3. Heat as a Driver of Change | 热作为变化的驱动力

Heat gives atoms and ions enough energy to vibrate and rearrange themselves into more stable crystal structures. The main sources of heat are nearby magma intrusions and the natural rise in temperature with depth.

热为原子和离子提供了足够的能量，使其振动并重新排列成更稳定的晶体结构。热的主要来源是附近的岩浆侵入体以及随深度增加而自然升高的温度。

Metamorphism often occurs between about 200 °C and 800 °C. These temperatures are high enough to change minerals but usually below the melting point of the whole rock.

变质作用通常发生在大约 200 °C 到 800 °C 之间。这些温度足以改变矿物，但通常低于整个岩石的熔点。

As temperature rises, tiny mineral grains may grow larger and interlock more tightly. This makes the rock harder and less porous.

随着温度升高，细小的矿物颗粒会长大并更紧密地互锁。这使得岩石更坚硬、孔隙更少。

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4. Pressure as a Driver of Change | 压力作为变化的驱动力

Deep burial and tectonic plate collisions produce enormous pressure. This pressure can squash mineral grains, make the rock denser, and force flat minerals to line up in parallel layers.

深层埋藏和板块碰撞会产生巨大的压力。这种压力会挤压矿物颗粒，使岩石更致密，并迫使片状矿物平行排列。

Directed pressure, which pushes harder in one direction than another, creates a layered or banded appearance called foliation. Slate, schist, and gneiss are well-known foliated metamorphic rocks.

定向压力在一个方向上的推动力比另一个方向更强，会形成称为叶理的层状或条带状外观。板岩、片岩和片麻岩是著名的叶理化变质岩。

Uniform pressure, which pushes equally from all sides, does not produce strong foliation. It usually results in non-foliated rocks such as marble and quartzite.

均匀压力从各个方向同等推动，不会产生明显的叶理。它通常形成非叶理化岩石，如大理岩和石英岩。

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5. Chemical Fluids and Mineral Change | 化学流体与矿物变化

Hot water and other fluids can flow through cracks and pores in rock during metamorphism. These fluids carry dissolved ions and can speed up chemical reactions that change one mineral into another.

在变质作用过程中，热水和其他流体会流经岩石的裂缝和孔隙。这些流体携带溶解的离子，并能加速将一种矿物转变为另一种矿物的化学反应。

For example, fluids may add silicon, iron, or magnesium to a rock, or remove elements such as calcium and sodium. This changes the overall chemistry of the rock.

例如，流体可能会向岩石中添加硅、铁或镁，或带走钙和钠等元素。这会改变岩石的整体化学成分。

heat + pressure + chemical fluids → new mineral structures

热、压力和化学流体共同作用，使原有矿物转变为新的矿物结构，而岩石不会熔化。

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6. No Melting: The Solid-State Reaction | 不熔化：固态反应

Unlike igneous rocks, metamorphic rocks form without the rock becoming liquid. Atoms move only short distances through the solid crystal lattice, so the rock remains solid throughout the process.

与火成岩不同，变质岩在形成过程中岩石不会变成液体。原子只在固态晶格中短距离移动，因此岩石在整个过程中始终保持固态。

Some original features of the parent rock may survive, such as bedding layers or fossils, although they are often squashed, stretched, or distorted.

母岩的某些原始特征可能会保留下来，例如层理或化石，尽管它们常常被压扁、拉长或扭曲。

If the temperature rises enough to melt the rock, the result is magma. When that magma later cools and solidifies, it forms an igneous rock, not a metamorphic rock.

如果温度升高到足以熔化岩石，就会产生岩浆。当岩浆后来冷却凝固时，形成的是火成岩，而不是变质岩。

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7. Contact Metamorphism | 接触变质作用

Contact metamorphism happens where hot magma rises and heats the cooler surrounding rock, called country rock. The baked zone around the intrusion is called a metamorphic aureole.

接触变质作用发生在炽热岩浆上升并加热周围较冷岩石（即围岩）的地方。侵入体周围受烘烤的区域称为变质晕。

This type of metamorphism is usually local and dominated by high temperature rather than high directed pressure. Therefore, the rocks are often non-foliated and have large interlocking crystals.

这种变质作用通常是局部的，以高温而非强定向压力为主。因此，岩石往往是非叶理化的，并具有大型互锁晶体。

Marble and quartzite are typical products of contact metamorphism because their parent rocks, limestone and sandstone, are baked by nearby magma.

大理岩和石英岩是接触变质作用的典型产物，因为它们的母岩石灰岩和砂岩被附近的岩浆烘烤。

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8. Regional Metamorphism | 区域变质作用

Regional metamorphism affects very large areas, often hundreds or thousands of square kilometres, during mountain building at convergent plate boundaries.

区域变质作用影响非常大的区域，通常达数百或数千平方公里，发生在汇聚板块边界造山运动期间。

Both high pressure and high temperature act together over a long period. This produces strongly foliated rocks with minerals arranged in visible bands.

高压和高温在长时间内共同作用。这会产生强烈叶理化的岩石，其矿物以可见的条带排列。

Slate, schist, and gneiss are typical regional metamorphic rocks. The degree of foliation and crystal size increases with temperature and pressure.

板岩、片岩和片麻岩是典型的区域变质岩。叶理化程度和晶体大小随温度和压力的增加而增大。

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9. Common Examples and Uses | 常见例子与用途

Different parent rocks produce different metamorphic rocks. The table below shows some common transformations.

不同的母岩会产生不同的变质岩。下表显示了一些常见的转变。

Parent rock | 母岩	Metamorphic rock | 变质岩	Main change | 主要变化
limestone | 石灰岩	marble | 大理岩	calcite crystals grow larger | 方解石晶体变大
shale or mudstone | 页岩或泥岩	slate | 板岩	clay minerals align into layers | 黏土矿物排列成层
sandstone | 砂岩	quartzite | 石英岩	quartz grains fuse together | 石英颗粒熔合在一起

Marble is used for statues, floors, and kitchen worktops because it is hard and can be polished. Slate is used for roofing tiles and the beds of pool tables because it splits into thin, flat sheets.

大理岩因坚硬且可抛光而被用于雕像、地板和厨房台面。板岩因能裂成薄而平的片材而被用作屋顶瓦和台球桌面。

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10. Key Ideas for Exam Success | 考试成功要点

For KS3 chemistry and Earth science exams, remember that metamorphic rocks are changed by heat, pressure, or chemical fluids, but they do not melt.

对于 KS3 化学和地球科学考试，请记住变质岩是由热、压力或化学流体改变而成的，但它们不会熔化。

• A metamorphic rock forms from a parent rock or protolith. | 变质岩由母岩或原岩形成。
• No melting occurs during metamorphism; if melting happens, an igneous rock forms. | 变质作用过程中不会发生熔化；如果发生熔化，则形成火成岩。
• Heat and pressure can cause minerals to recrystallise and grow larger. | 热和压力会使矿物重结晶并长大。
• Directed pressure produces foliated rocks such as slate, schist, and gneiss. | 定向压力产生叶理化岩石，如板岩、片岩和片麻岩。
• Limestone changes into marble, and shale changes into slate. | 石灰岩变成大理岩，页岩变成板岩。

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