The Rock Cycle

Activities to try

1. 1

   Transform and trace a rock through the cycle

   Why it works: The rock cycle has no fixed start or end: material can route between igneous, sedimentary and metamorphic forms depending on conditions, and these transformations happen over geological time far beyond a human lifetime, which is why we rarely see them occur. The cycle is kept turning by two energy engines — the Sun powering surface weathering, erosion and deposition, and Earth's internal heat powering melting, metamorphism and uplift.

   1. Start with a chunk of granite and choose a process to apply to it: 'weather and erode', 'bury and compact', 'heat and squeeze', 'melt', or 'cool'.
   2. Watch the sample transform as each process is applied — granite crumbles to sand, sand becomes layered sandstone, sandstone recrystallises under heat and pressure into a metamorphic rock such as quartzite (note that limestone would instead give marble and mudstone would give slate), melting gives magma, and cooling gives new igneous rock — with the rock renamed and its texture redrawn at each step (interlocking crystals for igneous rock, layers for sandstone, and tightly interlocking recrystallised grains for quartzite, which is usually not banded).
   3. Trace your own chosen path through the loop and record the sequence of rocks and processes you passed through.
   4. Attempt a 'get me from granite to marble' challenge: find and record a valid route (routing through a limestone/carbonate parent to reach marble), and check whether your route is one of several possible paths.
   5. Note the elapsed time counter that ticks up, typically by thousands to millions of years for most steps (lava cooling at the surface can be much quicker), and compare that to a human lifetime.
2. 2

   Classify, match and sequence rock-cycle knowledge

   Why it works: Each rock class is tied to a specific forming process and concrete example, and a valid cycle path is an ordered sequence of those processes.

   1. Sort granite, basalt, limestone, sandstone, marble and slate into the three classes: igneous, sedimentary, metamorphic.
   2. Match each rock example to its formation process (cooled magma/lava; sediment — rock fragments, shells or minerals settling out of water — compacted and cemented; existing rock changed by heat and pressure without melting).
   3. Order the steps of a granite-to-new-igneous-rock journey into a valid sequence.
   4. Answer: which process makes metamorphic rock? (heat + pressure, without melting).
   5. For granite and basalt, decide which cooled slowly at depth (large crystals) and which cooled fast at the surface (small crystals).
3. 3

   Explore a rock-cycle diagram and rock textures

   Why it works: Rocks carry visible evidence of how they formed, and a diagram plus real samples anchors the vocabulary, processes and spatial setting (depth of burial, cooling) of the cycle.

   1. Tap each rock type and each arrow on a rock-cycle wheel to reveal the process it represents, an example rock, and a photo of its texture.
   2. Compare texture cues across classes: interlocking crystals, large or too small to see (igneous); layers, rounded grains or fossils (sedimentary); banding or foliation in some metamorphic rocks (e.g. gneiss), thin splitting sheets in slate, and a sugary mass of interlocking crystals in marble or quartzite. Note that marble and quartzite also have interlocking crystals, so use more than one cue.
   3. Use a crust cross-section view to see where burial, heat and pressure at depth, and rising/cooling magma occur, and how crystal size relates to cooling depth.
   4. Where possible, handle real rock samples (granite, basalt, limestone, sandstone, marble, slate) and match each to its class using the texture cues.