📚 Igneous Rock | 火成岩
Igneous rocks are the frozen evidence of Earth’s fiery interior. They form when molten rock cools and solidifies, and their textures and minerals tell us how and where that cooling happened. In this KS3 chemistry topic, you will learn how igneous rocks are classified, why crystal size matters, and how these rocks fit into the wider rock cycle.
火成岩是地球炽热内部的冻结证据。它们由熔融岩石冷却凝固而成，其结构和矿物告诉我们冷却发生的方式和地点。在这个 KS3 化学主题中，你将学习火成岩的分类、晶体大小为何重要，以及这些岩石如何融入更广泛的岩石循环。
1. What Is Igneous Rock? | 什么是火成岩？
Igneous rock is one of the three main rock types, alongside sedimentary and metamorphic rock. The name comes from the Latin word ‘ignis’, meaning fire. Igneous rock forms when molten rock material called magma, if it is below the surface, or lava, if it is on the surface, cools and solidifies.
火成岩是三大岩类之一，另外两类是沉积岩和变质岩。这个名字来自拉丁语 ‘ignis’，意思是火。当地下的岩浆或地表的熔岩冷却凝固时，就形成火成岩。
2. From Magma to Rock | 从岩浆到岩石
Deep inside the Earth, temperatures are high enough to melt rock. This molten mixture of minerals, dissolved gases and sometimes solid crystals is called magma. When magma reaches the surface through a volcano or crack, it is called lava. Cooling turns this liquid rock into solid igneous rock.
地球深处温度很高，足以熔化岩石。这种由矿物、溶解气体和有时固体晶体组成的熔融混合物称为岩浆。当岩浆通过火山或裂缝到达地表时，就称为熔岩。冷却使这种液态岩石变成固态火成岩。
3. Intrusive Igneous Rocks | 侵入岩
Igneous rocks that form below the Earth’s surface are called intrusive or plutonic rocks. Magma cools slowly underground because the surrounding rock acts as an insulator. Slow cooling gives large mineral crystals time to grow. Granite is a common intrusive igneous rock.
在地表以下形成的火成岩称为侵入岩或深成岩。由于周围岩石像隔热层一样，岩浆在地下冷却得很慢。缓慢冷却让大矿物晶体有时间生长。花岗岩是一种常见的侵入岩。
4. Extrusive Igneous Rocks | 喷出岩
Igneous rocks that form on the Earth’s surface are called extrusive or volcanic rocks. Lava cools quickly when exposed to air or water. Rapid cooling only allows small crystals to form, and sometimes no crystals form at all. Basalt is a common extrusive igneous rock.
在地表形成的火成岩称为喷出岩或火山岩。熔岩暴露在空气或水中会迅速冷却。快速冷却只允许形成小晶体，有时甚至完全不形成晶体。玄武岩是一种常见的喷出岩。
5. Crystal Size and Cooling Rate | 晶体大小与冷却速率
There is a simple relationship between cooling rate and crystal size. Slow cooling produces large crystals because ions have more time to arrange into an orderly lattice. Fast cooling produces small crystals or glass because ions are frozen before they can form large structures.
冷却速率与晶体大小之间有一个简单关系。缓慢冷却产生大晶体，因为离子有更多时间排列成有序晶格。快速冷却产生小晶体或玻璃，因为离子还没来得及形成大结构就被冻结。
Cooling rate ↑ → Crystal size ↓ | 冷却速率 ↑ → 晶体大小 ↓
6. Common Examples: Granite and Basalt | 常见例子：花岗岩和玄武岩
Granite is a light-coloured intrusive rock. It contains large interlocking crystals of quartz, feldspar and mica. Granite is hard and resistant to weathering. Basalt is a dark extrusive rock with small crystals. It is the most common rock in the ocean floor.
花岗岩是一种浅色侵入岩。它含有石英、长石和云母的大型互锁晶体。花岗岩坚硬且抗风化。玄武岩是一种深色喷出岩，晶体很小。它是海底最常见的岩石。
7. Glassy and Frothy Igneous Rocks | 玻璃质和泡沫状火成岩
Some lava cools so fast that no crystals form. Obsidian is a natural volcanic glass that breaks with sharp, curved edges. Pumice forms when gas bubbles are trapped in rapidly cooling lava. It is so full of holes that it can float on water.
有些熔岩冷却得太快，没有晶体形成。黑曜岩是一种天然火山玻璃，断裂时形成锋利的弯曲边缘。浮岩是气体气泡被困在快速冷却的熔岩中形成的。它充满气孔，因此可以漂浮在水面上。
8. Mineral Composition and Colour | 矿物成分与颜色
The minerals in igneous rock affect its colour. Rocks rich in silica, such as granite and rhyolite, tend to be light-coloured. Rocks with less silica and more iron and magnesium, such as basalt and gabbro, tend to be dark-coloured. Geologists use colour as a first clue to composition.
火成岩中的矿物影响其颜色。富含二氧化硅的岩石，如花岗岩和流纹岩，往往颜色较浅。二氧化硅较少而铁和镁较多的岩石，如玄武岩和辉长岩，往往颜色较深。地质学家把颜色作为判断成分的第一条线索。
9. Igneous Rocks in the Rock Cycle | 岩石循环中的火成岩
Igneous rock is the starting point of the rock cycle. Weathering and erosion break it into sediments, which can form sedimentary rock. Heat and pressure can change any rock into metamorphic rock. If buried deep enough, rock can melt again and restart the cycle as magma.
火成岩是岩石循环的起点。风化和侵蚀把它破碎成沉积物，沉积物可以形成沉积岩。热和压力可以把任何岩石变成变质岩。如果埋得足够深，岩石会再次熔化，以岩浆的形式重新开始循环。
10. Uses of Igneous Rocks | 火成岩的用途
Many igneous rocks are useful building materials. Granite is used for countertops, flooring and monuments because it is hard and attractive. Basalt is crushed to make road stone and railway ballast. Pumice is used in cleaning products and lightweight building blocks.
许多火成岩是很有用的建筑材料。花岗岩用于台面、地板和纪念碑，因为它坚硬美观。玄武岩被压碎用于铺路石和铁路道砟。浮岩用于清洁产品和轻质建筑砌块。
11. Key Summary Table | 重点总结表
Use this table to compare intrusive and extrusive igneous rocks.
用这个表格比较侵入岩和喷出岩。
| Feature 特征 | Intrusive 侵入岩 | Extrusive 喷出岩 |
| Where formed 形成位置 | Underground 地下 | Above ground 地表 |
| Cooling rate 冷却速率 | Slow 慢 | Fast 快 |
| Crystal size 晶体大小 | Large 大 | Small or none 小或无 |
| Texture 结构 | Coarse 粗粒 | Fine or glassy 细粒或玻璃质 |
| Examples 例子 | Granite, gabbro 花岗岩、辉长岩 | Basalt, obsidian, pumice 玄武岩、黑曜岩、浮岩 |
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