Rock Cycle: Processes of Rock Formation and Erosion

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Preliminary Concepts

  • Igneous: this rocks form as liquid magma or lava cools; the crystals that form are interlocking
  • Metamorphic: this rock forms from existing (not molten) rocks under heat and/or pressure; the crystals are interlocking and have a preferred orientation
  • Sedimentary: rocks are cemented together; not formed from crystals but from pieces or precipitants

Misconceptions about the rock cycle:

  • One common misconception is that layered rocks are always sedimentary; in fact, many metamorphic rocks are layered, and even a few igneous rocks can have layers.
  • Some students mistakenly assume that one type of rock can only change to another type; for example, that igneous can only change to sedimentary or metamorphic rather than melting again and changing to another type of igneous rock.
  • Students may think that metamorphic rocks are a “little melted” when, in fact, if there is melting, then the process is igneous.
  • Students may think that metamorphic rocks require both heat and pressure, when there are cases of metamorphism that are just heat or predominantly pressure.
  • Students may assume that any amount of pressure or heat will cause a rock to metamorphosize, when there are specific amounts; some pressure may just make a sedimentary rock, while too much heat will melt a rock, resulting in an igneous process.


Sorting rocks: sedimentary/igneous/metamorphic

Igneous activities
  • Cake batter lava
    Students compare the viscosity of two different lava flows, which model the differences between thick sticky rhyolitic (granite) composition and runny basaltic (basalt) composition
  • Lava Layering
    Students make and map a volcano with many different eruptions, then trade and investigate the history of another team’s volcano through core samples and road cuts.
Erosion and weathering activities
Students wear down frozen sand “rocks” using water.
Metamorphic activities
  • Modeling metamorphic processes
    Students model the formation of a metamorphic rock with playdough and elongated “minerals” — we used orzo pasta instead of almond slivers.