Rock Cycle - Rocks (3A)
Pre Lab 

  • Comparing sedimentary, igneous, and metamorphic rocks.
  • Exploring the etymology of sedimentary, igneous, and metamorphic.
  • igneous
  • metamorphic
  • sedimentary

Students learn the meaning of the words igneous, sedimentary, and metamorphic.

Schist, a metamorphic rock in thin section. 


Minerals make up rocks. Rocks are formed in many environments upon and within the Earth's crust. There are three types of rock, each formed in a different way. Igneous rock , formed by the cooling of magma (molten rock) inside the Earth or on the surface. Sedimentary rocks, formed from the products of weathering by cementation or precipitation on the Earth’s surface. Metamorphic rocks, formed by temperature and pressure changes inside the Earth. All three types of rock make up the Earth’s lithosphere, the outermost layer. The lithosphere averages about 100 kilometers in thickness.

All igneous rocks began as magma (molten rock) which cooled and crystallized into minerals. Geologists classify igneous rocks based on both their crystal size and composition. Igneous rocks may look different because they may have cooled at different rates and the "mother" magma (original melted rock) was of a different composition. Variations in these two factors have created many different types of igneous rocks. When the magma cools at different rates, it creates different sized minerals. Quick cooling magmas have small minerals (with the exception of obsidian, which is actually composed of silica, but has no crystalline structure). Basalt, for example, has small minerals, most of which can only be seen under a microscope. Quick cooling lavas are called volcanic rocks. Magma that cools slowly creates rocks like granite, which have large minerals that can be seen with the naked eye. These igneous rocks cool inside the lithosphere, and are called plutonic rocks.

Sedimentary rocks form at the Earth’s surface in two main ways. Clastic material (pieces of other rocks or fragments of skeletons) may become cemented together and chemical precipitation and evaporation can form sedimentary rocks. Sedimentary rocks are usually associated with liquid water (which facilitates erosion, transportation, deposition, and cementation). However, sedimentary rocks may also form in dry, desert environments or in association with glaciers.

Metamorphic rocks are igneous, sedimentary, or preexisting metamorphic rocks that have been changed by great pressures and temperatures within the crust and upper mantle of the Earth. The temperatures were not enough to melt the rock, otherwise, an igneous rock would have formed. The pressures were much greater than those required to simply break the rocks into pieces. They were high enough to change the chemical make up of the rock by forcing the elements in it to "exchange partners." Different grades of temperature and pressure will cause the same original rock to form very different metamorphic rocks. Slate, which forms from the sedimentary rock shale, is very dense, smooth and does not contain visible minerals. However, if more pressure and temperature are applied to a slate, it could turn into schist, which has visible layers of minerals. If yet higher temperature and pressure are applied, the schist could turn into gneiss, which shows visible bands of minerals.

  1. Review with students where igneous, sedimentary, and metamorphic rocks are formed using the diagram below.

  1. Ask students to find words which have ign-, sediment-, and metamorphor- roots. This may wish to use children’s dictionaries, encyclopedias or other similar resources. This will help the students remember the meaning of the words igneous, sedimentary, and metamorphic. Here are some examples, along with suggestions for how to explain rocks to the students.

    IGNEOUS -Fire or hot rocks, form when melted rock (magma or lava) cools. When magma cools slowly, large minerals are produced. In lava that cools quickly the minerals can only be seen with a microscope. IGN = Latin for fire

    ignis fatuus

    SEDIMENTARY - Sedimentary rocks are usually formed under water when grains of broken rocks are glued together. SEDIMENT = Latin meaning to settle


    METAMORPHIC - Metamorphic rocks are rocks that once were igneous or sedimentary rocks but have been changed by pressure and temperature. META = from Latin and Greek meaning to transform; MORPH = Greek meaning form


  2. Students can also develop nicknames for the rocks, and they can call the individual types of rocks: IGNEOUS - fire or hot; SEDIMENTARY - cool, wet, fossil; METAMORPHIC - flat, squished, changed
  3. Using the Mineral and Rock Kit, show the students examples of the different types of rocks. Use the rocks in the kit to see if students remember what formed each of them. The written packet included with the kit should be consulted for more information on each rock.

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