--- title: "The Rock Cycle" description: "Explain how igneous rocks form when molten rock cools, sedimentary rocks form through processes including compaction, cementation and mineral deposition, and metamorphic rocks form through heat and pr" canonical: https://lightmysky.com/learn/science/the-rock-cycle-mt_NckKLZ3uCE source: https://lightmysky.com/learn/science/the-rock-cycle-mt_NckKLZ3uCE.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # The Rock Cycle Explain how igneous rocks form when molten rock cools, sedimentary rocks form through processes including compaction, cementation and mineral deposition, and metamorphic rocks form through heat and pressure without melting. Trace possible routes between rock types over geological time. Subject: Science · Area: Matter & Materials · Ages 12 to 14 Page: https://lightmysky.com/learn/science/the-rock-cycle-mt_NckKLZ3uCE ## Ready when they can - Describes how each rock type (igneous, sedimentary, metamorphic) is formed - Gives an example of each rock type and its formation (e.g. granite, limestone, marble) - Traces a rock sample through possible transitions in the rock cycle - Explains geological time and why many rock-cycle changes are slow, while some stages can happen much faster ## Lesson: The Rock Cycle Rocks are grouped by how they formed. Igneous rock forms when molten rock cools and solidifies. Sedimentary rock can form when sediment is compacted and cemented, or when minerals come out of water. Metamorphic rock forms when heat and pressure change existing rock without melting it. The rock cycle describes possible changes between these groups. There is no required order. *(drawing: Read across, then continue on the next row. This is one possible route, not a required trip for every rock.)* Molten rock underground is called magma. At the surface it is called lava. Slow cooling underground gives crystals time to grow large, as in granite. Rapid cooling near the surface usually produces small crystals, as in basalt. Very rapid cooling can produce glass with no crystals. Crystal size can help you infer how an igneous rock cooled. **Example.** Weathering breaks down rock where it is. Erosion moves the material, and deposition leaves it in a new place. Buried sediment can be compacted by weight above it and cemented by minerals between its grains. Sand can become sandstone. Many limestones form from calcium carbonate shells and skeletons; others form when calcium carbonate comes out of water. Limestone is sedimentary rock. Heat and pressure underground can cause its minerals to recrystallise into interlocking crystals, forming marble. Marble is metamorphic rock. It stays solid during this change. If limestone melts instead, it becomes molten material; cooling that material would make igneous rock, not marble. Any rock type can weather into sediment. Any rock type can also melt under suitable conditions, and the molten material can cool into igneous rock. Further heat and pressure can change metamorphic rock again. There is no final rock type. For example, marble exposed at the surface can weather into sediment instead of melting. Geological time covers Earth's long history, including spans of millions and billions of years. Building thick sediment layers, burial and mountain formation often take very long periods. Some stages are faster: erupted lava can solidify within a human lifetime. A rock has no fixed timetable, and a marble sample alone cannot tell you exactly how long its formation took. **Recap.** Cooling forms igneous rock. Sedimentary processes form sedimentary rock. Heat and pressure change solid rock into metamorphic rock. Routes and timescales vary. *Lesson, questions and flashcards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Properties of rocks](https://lightmysky.com/learn/science/properties-of-rocks-mt_R6YoRXkRxS) ## Optional connections - [How Tectonic Plates Move](https://lightmysky.com/learn/science/how-tectonic-plates-move-mt_gv_uoHkdjR) - [Rocks and soil](https://lightmysky.com/learn/science/rocks-and-soil-mt_yhhprm7dZK) - [How Rocks Change Over Time](https://lightmysky.com/learn/science/how-rocks-change-over-time-mt_z7AJZapsJj) ## Opens up - [Minerals and the Three Rock Families](https://lightmysky.com/learn/science/minerals-and-the-three-rock-families-mt_S0edEKh084)