Geology Vocabulary in English

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.

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.

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.

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".

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.

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.

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.

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.

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.

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.