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IGNEOUS ROCKS Heat from the interior of the earth can make rock hot enough to melt. Molten (melted) rock that is inside the earth is called magma. If magma is pushed to the surface where we can see it, we then call the molten rock lava. Remember that particles of a liquid can roam around freely because they are not bonded to each other to form a definite shape. When magma or lava cools, the atoms begin to stick to each other to form solid chunks. Sometimes this happens v-e-r-y s-lo-w-l-y. Magma deep inside the earth can cool and solidify over a period of hundreds or even thousands of years! Slow cooling can give individual atoms time to “line up” and form definite patterns called crystalline structures. This allows large, beautiful crystals to form. Granite is an example of a rock with large crystals that grew slowly because of slow, steady cooling. When molten rock—particularly lava—cools quickly (like when volcanic pahoehoe lava cools when it touches ocean water), the atoms “freeze” into place without having time to “line up” and form large crystals. The solids that form may have small crystals or even no crystals at all. If there is no definite pattern to how the atoms link together, the result is an amorphous solid. Obsidian—a glassy volcanic material—is an example of a rock that is amorphous. Choose the best ending for this sentence: Igneous rocks are formed in a way that is similar to the formation of ______________________ . A. Rice Krispy bars C. chocolate bars B. a milkshake D. tortillas Look at the Box of Rocks. Remove and examine the rocks that are labeled “1” through “6.” These are all igneous rocks—rocks that formed from cooling magma or lava. On the back of this page, arrange the six igneous rocks into their correct spots in the table. IGNEOUS ROCKS (#1-6) NAME OBSIDIAN (ob-SIH-dee-un) BASALT (buh-SAULT) GABBRO (GA-broe) GRANITE (GRA-nitt) PORPHYRY (PORR-furr-ree) PUMICE (PUH-miss) DESCRIPTION Black, shiny and glassy, the sharp edges can cut (Be careful!)/ Strange “shell-shaped” surfaces where it has been broken up. Obsidian is made by quick-cooling lava. There was not enough time for the atoms to “line up” neatly and form large crystals. Dark gray (almost black), dull, tiny crystals, dense, no air pockets, made by cooling lava. Crystals could grow, but they did not get large. Much of the oceanic crust is basalt, formed at mid-ocean ridges. Mostly dark, large shiny crystals, dense, no air spaces. Chemically similar to basalt, but gabbro has larger crystals because it is made by slower-cooling magma. Much of the oceanic crust is gabbro, formed at mid-ocean ridges. Black and white “salt and pepper”, large crystals, dense, no air spaces. Like gabbro, granite is formed from cooling magma, but the magma is chemically different, leading to the formation of lighter-colored mineral crystals such as quartz and pink or white feldspars. A few big crystals surrounded by many crystals that are much smaller. This was magma that at first cooled slowly (making large crystals), and then more quickly (making the smaller crystals). Nearly white, dull “chalky” look, cannot see individual crystals, very low density due to millions of tiny air pockets. Made by lava shot out of volcanoes. The gas bubbles formed before the lava could solidify. Pumice can float on water! PUT IT HERE! SEDIMENTARY ROCKS Wind, water, ice, sunlight and gravity all cause rock to weather into smaller pieces. Through the process of erosion, these rock and mineral pieces, called sediments, are moved from one place to another. Eventually, the sediment is deposited in layers. As the new layers of sediment are deposited, they cover older layers. Older layers become squeezed and compacted by all the weight of the sediments on top. Dissolved minerals in the ground water can act as “glue” and cement the pieces of sediment together. The result is a new rock that is made out of the sediments of older rocks (or even broken seashells!). This new substance is a sedimentary rock. Sandstone is a sedimentary rock that formed when pieces of sand were cemented together. Limestone is a sedimentary rock that formed when pieces of seashell were cemented together. There is another way that sedimentary rocks can form. Sometimes water containing a lot of dissolved mineral atoms will evaporate. When evaporation occurs, water molecules jump into the air and leave the mineral atoms behind. The mineral atoms begin sticking to each other to form crystals. Table salt (NaCl) is a sedimentary rock that formed when sea water evaporated and left atoms of sodium and chlorine behind. Choose the best ending for this sentence: Many sedimentary rocks are formed in a way that is similar to the formation of _________________ . A. Rice Krispy bars C. chocolate bars B. a milkshake D. tortillas Look at the Box of Rocks. Remove and examine the rocks that are labeled “7” through “11.” These are all sedimentary rocks. On the back of this page, arrange the five sedimentary rocks into their correct spots in the table. SEDIMENTARY ROCKS (#7-11) NAME DESCRIPTION SHALE Dark, fine-grained, formed by mud or clay (i.e. mixtures of tiny rock particles and water) that was pressed together for millions of years. SANDSTONE Light colored, sometimes in layers, feels like sandpaper and bits of sand can be rubbed off (Don’t overdo it!). Made by sand particles (often quartz) that have been pressed and stuck together (like how Rice Crispy bars are made). LIMESTONE Medium gray, dull, finegrained. Limestone is mostly made of the mineral calcite. It was made from ocean sediments (usually sea shells) that piled up and stuck together. A rock made of older pebbles, gravel, sand and clay. The individual pieces of sediment have a rounded appearance because they were worn smooth in river beds. CONGLOMERATE (conn-GLOMM-ur-ett) HALITE (SALT) (HAY-lite) Colorless, transparent, with right-angle sides. When the salty water of ancient seas evaporated, the sodium and chlorine atoms that were left behind joined to form these large, beautiful crystals. Humans mine this rock, grind it up, and put it in salt shakers. PUT IT HERE! METAMORPHIC ROCKS When a tadpole changes into a frog, or when a caterpillar changes into a moth or butterfly, this process of change is called metamorphosis. “Meta” means change and “morph” means form, so a metamorphosis is a “change of form.” Rocks can also undergo metamorphosis. This can happen when rocks are squeezed and/or heated enough to make them almost, but not quite, liquid. Under great heat and/or pressure, the individual atoms of the rock may migrate (move) a short distance and very slowly, and then combine in new ways. The result is a metamorphic rock—a rock that has changed in structure due to heat and pressure (but without actually melting). Choose the best ending for this sentence: Many metamorphic rocks are formed in a way that is similar to the formation of _________________ . A. Rice Krispy bars C. chocolate bars B. a milkshake D. tortillas Look at the Box of Rocks. Remove and examine the rocks that are labeled “12” through “16.” These are all metamorphic rocks. On the back of this page, arrange the five metamorphic rocks into their correct spots in the table. When you do so, compare them with the rocks that they “used to be” before they metamorphosed. METAMORPHIC ROCKS (#12-16) NAME SLATE DESCRIPTION Dark bluish-gray, in fine layers, dense, no air pockets. Formed by metamorphosed shale. Set a piece of shale here SCHIST (shist) for comparison! Dark and light, sparkly, slightly in layers. Formed by metamorphosed slate (which was shale before that). Compare with slate, which is one space higher up in this table.. MARBLE Usually white or light and ”sugary,” sometimes with stripes. Formed by metamorphosed limestone. Set a piece of limestone here QUARTZITE (KWORTS-ite) for comparison! Usually reddish, pinkish or purplish. Formed by metamorphosed sandstone. Set a piece of sandstone here GNEISS (nice) for comparison! Black and white (or black and pink) bands or layers, small crystals, dense, no air pockets. Often formed by metamorphosed granite. Set a piece of granite here for comparison! PUT IT HERE! IN THE METAMORPHIC PAGE, USE THE WORD ‘RECRYSTALLIZATION’ TO MATCH ITS USE IN THE ROCK CYCLE GAME CARDS.