Geology Vocabulary Quiz
12 multiple-choice questions on geology and earth science vocabulary: igneous, sedimentary and metamorphic rocks, minerals, plate tectonics, fossils, erosion, magma and strata. B2–C1 level.
Geology Vocabulary — FAQ
Geologists classify rocks into three main types based on how they form. Igneous rocks form when molten rock (magma or lava) cools and solidifies — granite and basalt are examples. Sedimentary rocks form when layers of sediment (sand, mud, shells) are compressed and cemented together over time — sandstone, limestone and shale are examples. Metamorphic rocks form when existing rocks are transformed by intense heat and pressure deep in the Earth — marble (from limestone) and slate (from shale) are examples.
Magma and lava are both molten (liquid) rock, but the difference is location. Magma is molten rock that is still beneath the Earth's surface, within the crust or mantle. When magma erupts from a volcano and flows out onto the surface, it is called lava. So it is the same material, simply given a different name depending on whether it is below ground (magma) or above ground (lava). When lava cools, it solidifies into igneous rock.
A mineral is a naturally occurring, solid, inorganic substance with a definite chemical composition and an orderly internal (crystalline) structure — examples include quartz, feldspar, mica and calcite. A rock is a solid mass made up of one or more minerals (or, occasionally, organic material). For example, granite is a rock made mainly of the minerals quartz, feldspar and mica. In short, minerals are the building blocks, and rocks are made from them.
Tectonic plates are the large, rigid slabs that make up the Earth's outer shell (the lithosphere). They float on the softer, partly molten rock of the mantle beneath and move very slowly — only a few centimetres a year. Where plates meet, at 'plate boundaries', they can pull apart, push together or slide past one another. This movement, known as plate tectonics, causes earthquakes, builds mountains and creates volcanoes. The theory explains much of the Earth's geological activity.
A fossil is the preserved remains or traces of a living organism from the distant past — such as bones, shells, leaves or footprints. Most fossils form when an organism is quickly buried by sediment; over millions of years, the sediment hardens into sedimentary rock, and minerals gradually replace the original material, turning it to stone (a process called 'petrification' or 'mineralisation'). Fossils help geologists date rock layers and understand the history of life on Earth — a field called palaeontology.
Weathering is the breaking down of rocks in place, where they are, by physical forces (such as frost or temperature changes), chemical reactions (such as acid rain) or biological action (such as plant roots). Erosion is the next step: the wearing away and transport of those broken-down materials by moving agents such as water, wind, ice (glaciers) or gravity. In short, weathering breaks rock apart, and erosion carries the pieces away to be deposited somewhere else.
'Strata' (singular: 'stratum') are the distinct layers of sedimentary rock that build up over time, each representing a period of deposition. You can often see them as horizontal bands in a cliff or quarry. The study of these layers is called 'stratigraphy'. Because deeper layers are usually older than those above them (the 'law of superposition'), strata act like the pages of a history book, allowing geologists to read the sequence of past events and to date the rocks relative to one another.
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 can be vertical, horizontal or a combination of both. Faults usually occur near plate boundaries, where stress builds up in the rock; when the rock suddenly slips, the released energy causes an earthquake. The famous San Andreas Fault in California is an example where two tectonic plates slide past one another.
Sediment is loose material — fragments of rock, sand, mud, silt, shells or organic matter — that has been broken down by weathering and transported by water, wind or ice before being deposited. Sedimentary rock forms when these loose sediments are buried, compacted and cemented together over long periods (a process called 'lithification'). So sediment is the raw, loose material, while sedimentary rock is the solid rock it eventually becomes — for example, sand becoming sandstone.
The Earth has three main layers. The crust is the thin, solid, rocky outer layer on which we live — thicker under continents and thinner under oceans. Beneath it lies the mantle, a very thick layer of hot, dense, partly molten rock that slowly flows and drives the movement of tectonic plates. At the centre is the core, made mainly of iron and nickel: a liquid outer core (whose motion generates the Earth's magnetic field) and a solid inner core. Temperature and pressure increase greatly with depth.