Types of Rock

Activities to try

1. 1

   Run the rock factory: make each type and test what survives

   Why it works: A rock's type is its formation story, and fossils are found mainly in sedimentary rock because gentle layering can trap and preserve remains, while melting (igneous) destroys them and intense heat/pressure (metamorphic) usually destroys or distorts them.

   1. At a 'melt' step, cool a glowing lava/magma pool and watch crystals lock together, forming igneous rock.
   2. At a 'layers' step, drop layers of sand and mud with a small shell tucked between them, press them down to make sedimentary rock, then split it open to reveal the shell as a fossil. (In real rock, hardening the layers and turning a shell into a fossil takes a very long time.)
   3. At a 'heat and squeeze' step, take an existing rock and increase heat and pressure until it changes, for example its minerals lining up in bands, forming metamorphic rock (many, though not all, metamorphic rocks show bands).
   4. Try to preserve a shell in each process: drop it into the lava, put it through the heat-and-press, and set it among gentle layers — observe which process preserves it and which destroy it.
   5. State in your own words why fossils are found mainly in sedimentary rock: why melting in igneous rock destroys them, and why heat and pressure in metamorphic rock usually destroy or squash them.
2. 2

   Hand-lens classification of real specimens

   Why it works: Rocks can be compared and grouped by their appearance and simple physical properties, and the observable texture (crystals, grains, layers, bands, fossils) is evidence of how the rock formed.

   1. Examine real rock specimens such as granite, sandstone or chalk, and marble or slate with a hand lens.
   2. Look for distinguishing clues: interlocking crystals, loose grains, visible layers, embedded fossils, or bands/stripes (foliation).
   3. Sort the specimens into igneous, sedimentary, and metamorphic based on what you observe, then say which clue led to each decision. (Note crystals can appear in both igneous rock such as granite and some metamorphic rock such as marble. Marble usually has no bands, so compare the crystals instead: granite has mixed colours, marble is mostly one pale colour. With an adult, you can also check whether it fizzes in vinegar.)
   4. Where possible, link to local examples such as building stones or gravestones.
3. 3

   Natural rock or made by people?

   Why it works: Brick, concrete and tarmac are human-made materials, not natural rock, even though they can look rock-like.

   1. Look at a mixed set including natural rocks (granite, sandstone) and manufactured materials (brick, tarmac, concrete).
   2. Sort each item into 'natural rock' or 'made by people'.
   3. Give a reason for each sort, focusing on whether the material formed by a natural process or was manufactured.