Geology Vocabulary in English
20 essential geology words with definitions and example sentences — rocks, erosion, and earth science for B2–C1 ESL learners.
Geology vocabulary appears throughout science textbooks, nature documentaries, and academic writing about the earth. Terms such as igneous, erosion, and tectonic plate are essential for anyone reading about landscapes, natural disasters, or earth science in English. For B2 and C1 learners, mastering these words unlocks a whole field of academic and current-affairs reading.
This page covers 20 key geology words used to describe rocks, the processes that shape the land, and the structure of the earth. These terms appear in geography courses, IELTS reading passages, and news stories about earthquakes and volcanoes. You will encounter them in museum displays, hiking guides, and discussions about the natural world.
Unlike our broader Science vocabulary and Nature vocabulary pages, this list focuses specifically on the solid earth — its rocks, its movements, and the forces that wear it away and build it up. Mastering this vocabulary will strengthen your scientific reading comprehension and help you describe landscapes and earth processes with confidence.
Word List
| Word / Phrase | Meaning | Example Sentence |
|---|---|---|
| sediment | solid particles such as sand, silt, and mud that settle and build up in layers | Over millions of years, layers of sediment hardened into solid rock. |
| igneous | (of rock) formed when molten magma or lava cools and solidifies | Granite is an igneous rock that cooled slowly deep beneath the surface. |
| metamorphic | (of rock) formed when existing rock is transformed by intense heat and pressure | Marble is a metamorphic rock created from limestone under great pressure. |
| erosion | the gradual wearing away and removal of rock and soil by water, wind, or ice | Coastal erosion has worn away several metres of cliff over the past decade. |
| tectonic plate | one of the giant slabs of the earth's outer shell that slowly move and interact with one another | Earthquakes often occur where one tectonic plate grinds against another. |
| fault | a crack or fracture in the earth's crust along which the rock has moved | The San Andreas Fault marks the boundary between two great tectonic plates. |
| strata | layers of sedimentary rock, each representing a different period of deposition (singular: stratum) | The exposed cliff revealed colourful strata laid down over millions of years. |
| mineral | a naturally occurring solid substance with a definite chemical composition; the building blocks of rocks | Quartz is one of the most common minerals found in the earth's crust. |
| fossil | the preserved remains or traces of a once-living organism, found within rock | The fossil of an ancient fish was discovered embedded in the limestone. |
| magma | molten rock beneath the earth's surface | Deep beneath the volcano, magma slowly builds up under enormous pressure. |
| crust | the thin, solid outer layer of the earth, on which we live | The earth's crust is thinnest beneath the oceans and thickest under mountain ranges. |
| weathering | the breaking down of rock in place by physical, chemical, or biological processes, without it being carried away | Frost weathering splits rock apart when water freezes and expands inside cracks. |
| glacier | a large, slow-moving mass of ice that shapes the land as it flows downhill | The glacier carved a wide U-shaped valley as it advanced over thousands of years. |
| seismic | relating to or caused by earthquakes or vibrations of the earth | Scientists use seismic waves to study the structure deep inside the planet. |
| deposition | the laying down of sediment that has been transported by water, wind, or ice | The slowing river caused deposition of sand and gravel along its inner bends. |
| outcrop | a place where solid rock is exposed at the surface rather than covered by soil | The geologists examined the rock outcrop on the hillside for fossils. |
| ore | a naturally occurring rock or mineral from which a valuable metal can be profitably extracted | Iron ore is mined and then smelted to produce steel. |
| basalt | a dark, fine-grained igneous rock formed from rapidly cooled lava | The famous columns of the Giant's Causeway are made of basalt. |
| limestone | a sedimentary rock made mainly of calcium carbonate, often containing fossils | Rainwater slowly dissolves limestone, forming caves and underground rivers. |
| subduction | the process by which one tectonic plate slides beneath another and sinks into the earth's interior | Subduction along the coast creates deep ocean trenches and powerful volcanoes. |
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Frequently Asked Questions
What is the difference between igneous and metamorphic rock?
These are two of the three main types of rock. Igneous rock forms when molten material — magma below the surface or lava above it — cools and hardens; granite and basalt are common examples. Metamorphic rock forms when an existing rock is changed by intense heat and pressure deep within the earth, without melting completely. For example, limestone turns into marble, and shale turns into slate. The third type, sedimentary rock, forms from layers of compacted sediment. Remembering how each type forms makes the vocabulary much easier to recall.
What is the difference between erosion and weathering?
The two words are closely related but not the same. Weathering is the breaking down of rock where it stands — for example, when water freezes in a crack and splits the rock apart, or when rain chemically dissolves it. Erosion is the next step: it is the process by which the loosened material is picked up and carried away by water, wind, or ice. In short, weathering breaks the rock down in place, and erosion transports it somewhere else. A useful way to remember it: weathering wears, erosion removes.
What is a tectonic plate?
A tectonic plate is one of the enormous, rigid slabs that make up the earth's outer shell. There are several major plates and a number of smaller ones, and they float slowly on the hotter, softer layer beneath, moving only a few centimetres a year. Where plates meet, they may pull apart, push together, or slide past one another, and these boundaries are where most earthquakes, volcanoes, and mountain ranges occur. The study of how these plates move is called plate tectonics, one of the central ideas in modern geology.
What is subduction?
Subduction is the process by which one tectonic plate slides beneath another and sinks down into the hot interior of the earth. It usually happens where a denser oceanic plate meets a lighter continental plate. As the descending plate sinks, it melts and feeds magma to volcanoes above, and the bending of the plates creates deep ocean trenches. Subduction zones are responsible for some of the world's most powerful earthquakes and most explosive volcanoes, such as those around the Pacific "Ring of Fire".
What is the difference between magma and lava?
Both words refer to molten rock, but the difference is location. Magma is molten rock while it is still below the earth's surface, sitting in a chamber beneath a volcano. Lava is the same material once it has erupted and flowed out onto the surface. So the same molten rock changes its name the moment it breaks through the ground: it is magma underground and lava above ground. Lava also cools much faster than magma, which is why it forms fine-grained rocks like basalt.
What are strata?
Strata are the visible layers of sedimentary rock, each one laid down at a different time. The singular form is stratum. You can often see strata clearly in a cliff face or the wall of a canyon, where bands of different colours and thicknesses stack on top of one another. Because lower layers are usually older than the ones above them, geologists read strata almost like the pages of a book to work out the history of an area. The study of rock layers is called stratigraphy.
What is a fault in geology?
A fault is a fracture or crack in the earth's crust along which blocks of rock have moved relative to each other. The movement may be sudden, releasing energy as an earthquake, or very slow over long periods. Faults come in different types depending on the direction of movement, but they are all weak zones in the crust. Famous examples include the San Andreas Fault in California. Recognising the word fault in this geological sense is important, as it is quite different from the everyday meaning of a mistake.
What is an outcrop?
An outcrop is any place where the solid bedrock is exposed at the surface, rather than being hidden beneath soil, grass, or sand. Outcrops are extremely valuable to geologists because they offer a direct window into the rock beneath, allowing scientists to study its type, age, structure, and any fossils it contains. You will often find outcrops on hillsides, riverbanks, coastal cliffs, and road cuttings. The verb form, to outcrop, means for rock to appear at the surface in this way.
What is ore?
Ore is a naturally occurring rock or mineral that contains enough of a valuable metal — such as iron, copper, gold, or aluminium — to make it worth mining and extracting. Not every rock containing metal counts as ore; the concentration has to be high enough for extraction to be economic. Once ore is mined, it is processed and the metal is separated out, often by smelting. The word appears frequently in texts about mining, industry, and economics, so it is a useful term for advanced learners to know.
What is the best way to learn geology vocabulary?
The most effective approach is to group the words by theme — rock types (igneous, metamorphic, basalt, limestone), earth processes (erosion, weathering, deposition, subduction), and structure (crust, fault, strata, tectonic plate) — so that related terms reinforce one another. Read short articles or watch documentaries about volcanoes, mountains, and natural disasters in English, noting the words in context. Use Flash Cards on LexFizz to drill the 20 words on this page, then try describing a landscape or a recent earthquake in your own words.