Rock Cycle: The Hard Truth
Today’s science lesson was all about rocks! After briefly reviewing geology and the different layers of the Earth, students learned about the Rock Cycle and the three main categories of rocks (sedimentary, igneous and metamorphic). We discussed how all the rocks on the earth are constantly changing due to weathering, erosion, heat and pressure from within the Earth and noted such conditions on the Rock Cycle. We discussed some examples for each type of rock, observed and noted their distinct characteristics. In this regard, students pointed out that some igneous rocks (intrusive igneous rocks) consisted of easily visible minerals and were “coarsely grained,” whereas extrusive igneous rocks were fine grained. For sedimentary rock, we discussed how layers were formed in sedimentary rock and noted that fossils (discussed in a previous lesson) were found in some sedimentary rock. Finally, we discussed metamorphic rocks and how sedimentary or igneous rocks give rise to metamorphic rocks. Students also learned the differences between minerals and rocks and were introduced to Massachusetts’ state rock, the Roxbury Puddingstone ( a sedimentary rock) a stone used for building in the Boston/Roxbury area.
In the follow up activity, students pretended to be geologists and made observations about 10 rock samples they were given. Using a tool called a dichotomous key, students figured out the identity of the given rocks, based on their texture, color, mineral composition, and layering. Using knowledge obtained from the lesson and from a Rock Information chart students were able to classify each rock sample as either sedimentary, igneous, or metamorphic. Students were further ask to extend their classification of igneous rock, by distinguishing between intrusive and extrusive igneous rock.