Igneous rocks, such as basalt, gabbro, pumice and granite, form when rocks or sediment are exposed to the great heat of magma under the earth's crust. They are pushed to the surface during a volcanic eruption and are often difficult to chip or crack. Another sign that you have an igneous rock is the interlocking crystal pattern in the surface. Metamorphic rocks such as gneiss, slate, schist and marble form under intense heat and pressure conditions deep under the earth's surface. Look for a banded or wrinkled layer pattern to identify this rock type. Sedimentary rocks such as sandstone, mudstone and limestone form in strata layers from grains of sediment left by eroding rocks. A fossil is a sure sign that a rock is sedimentary. Sort through a collection of rocks with a rock guide in hand and classify each one as igneous, metamorphic or sedimentary.
A living illustration of the rock cycle lets children experience a "time-lapse" version of a process that takes thousands of years. Separate students into three stations and assign each group a rock type -- igneous, metamorphic or sedimentary. Set up other stations for weathering and erosion, compaction, melting, uplift and crystallization. Children take turns rolling dice or drawing cards to indicate what path in the rock cycle to take. For example, a sedimentary rock might draw a card that says, "An earthquake sucks you down into the hot magma," sending her to the melting station where another card sends her shooting out of a volcano to cool on the earth's surface and become an igneous rock. The igneous rock could be exposed to the eroding effects of wind and rain at the weathering station while another card decrees that the sediment gets buried in a landslide sending it to the compaction station to metamorphose under the great pressure. Every "rock" follows its own path depending on the fates drawn or rolled. A student must record his rock's journey through the phases of the rock cycle at each station.
Sugar cubes provide a good imitation of rock phases. Compare an untouched cube to sedimentary rock. Scrape it with the edge of a table knife to represent erosion. When the cube turns completely to powder, you have sediment. Pour the sediment into a foil boat to transport it to the heat source. Hold the boat with potholders and melt the sugar over a candle flame for the melting phase. As it cools and hardens, it represents igneous rock.
Literary and artistic students may enjoy turning a journey through the rock cycle into a story or cartoon with a personified rock character. Children can use creativity and imagination to bring the story to life with an exciting and adventurous plot to hold readers attention. Illustrations should add to the story and illustrate the processes in the rock cycle that serve as the setting and medium for intriguing plot twists and turns.