Rock Type Sorter – Free for Teachers and Parents

Use the free Rock Type Sorter below, right in your browser. No sign-up, no software to install, and nothing is sent to a server.

Rocks may look like simple stones, but every rock tells a story about how it formed, and geologists sort rocks into just three big families. This sorter practises that sorting with twelve well known rocks, asking you to decide whether each one is igneous, sedimentary, or metamorphic. Instant feedback turns each guess into a clue about heat, pressure, and time.

Igneous rocks form when molten rock cools and hardens. Deep underground, magma cools slowly and grows large crystals, producing rocks such as granite, which is speckled and strong enough for kitchen counters and monuments. Lava that erupts at the surface cools quickly, producing rocks such as basalt, which forms much of the ocean floor, and obsidian, a natural glass with sharp edges that early humans used for cutting tools.

Pumice is another igneous rock, and it is famous for being light enough to float, because gas bubbles were trapped in the lava as it cooled. That foamy texture is a strong clue, because no sedimentary or metamorphic rock looks quite like pumice. When you see a rock with visible crystals that interlock like a jigsaw, or a glassy surface formed by rapid cooling, igneous is usually the right family.

Sedimentary rocks form in layers, when sand, mud, pebbles, and the remains of living things settle, get buried, and are pressed and cemented together over long periods. Sandstone is made of sand grains, limestone often contains shells and can fizz with weak acid, shale splits into thin sheets of mud, and conglomerate looks like pebbles stuck in natural cement. If a rock shows layers or contains visible grains and pebbles, sedimentary is a strong bet.

Sedimentary rocks are also where fossils are usually found, because dead plants and animals can be buried gently in sediment before they decay completely. That is why a rock with a shell or a leaf impression almost always belongs to this family. Rivers, beaches, lakes, and shallow seas are the workshops where sedimentary rocks are made, grain by grain, layer by layer, over thousands or millions of years.

Metamorphic rocks form when an existing rock is changed by heat and pressure without melting completely. Marble is limestone that has been transformed, slate is shale that has been squeezed and heated, quartzite comes from sandstone, and gneiss shows banded patterns from intense pressure deep underground. The word metamorphic comes from a Greek word meaning change of form, which is a perfect summary of what happens.

A helpful sorting question is to ask how the rock was made, not just what it looks like. Was it cooled from melt, laid down in layers, or changed by heat and pressure? That question works better than memorising colours, because the same mineral can appear in different families. Marble and limestone, for example, are both pale and both contain similar minerals, yet one is metamorphic and the other is sedimentary, and only their formation story separates them.

Teachers can use this sorter alongside a small rock collection, asking learners to sort real samples before checking names on screen. Handling a piece of granite, sandstone, and slate gives a sense of weight, texture, and grain that pictures alone cannot provide. Learners can then explain each choice using the formation question, which moves the task from guessing to reasoning, the skill geologists actually use in the field.

The three families also connect in a larger story called the rock cycle. Igneous rocks weather into sediment that forms sedimentary rocks, sedimentary rocks can be buried and changed into metamorphic rocks, and metamorphic rocks can melt back into magma that cools as new igneous rocks. No rock family is a final resting place, and given enough time, heat, and pressure, every rock can change into another kind.

Sort a rock now, then try to say how it formed in one sentence before you check. The sorter needs no account and no download, and it runs entirely in your browser, so you can practise at school or at home as often as you like. That formation question, practised with twelve rocks, soon becomes a habit you can apply to any stone you pick up on a walk, a beach, or a mountainside.

Versión en español: Clasificador de Tipos de Rocas – Fácil y Gratis en Línea