Rocks Rosecke | Science 7

What is a rock? A rock is a natural, solid mixture of minerals or grains. Grains are the fragments that make up a rock. They can be many different sizes and shapes. The composition of the grains help determine the classification of rock.

Rock Terms Conglomerate Sandstone Composition of a rock is the kind of grains present in the rock. The texture of rock is the size of the grains and the way the grains fit together.

Igneous Rocks Formed from cooling Magma Intrusive – cools inside the earth Slow to cool – creates big crystals Extrusive – on the surface of the earth Fast to cool – creates small crystals

Sedimentary Rocks Formed when weather and erosion makes sediments that become compacted The size of the particles determines the type of rock.

Metamorphic Rocks Formed when other rocks are put under pressure and heat within the earth Foliated – alternating layers of different colors Nonfoliated – no layers of different colors

Physical Weathering When factors such as freezing, thawing, rain, waves, water pressure and winds work to break apart the rocks. These factors physically break the rock.

Chemical Weathering When minerals in the rocks are dissolved away by chemical reactions between rain water and whatever happens to be in the rock. Limestone and chalk are porous rocks that are effected by rainwater.

Biological Weathering When rocks are broken apart by living things. Insects and rodents burrow into the small cracks and make them bigger cracks. Trees, lichens, algae send roots into the cracks and as the plant grows it forces the cracks open. Humans walking, building, and digging (mining) break up lots of rocks.

Erosion Not just the breaking apart of rocks, but the movement of the broken material to another location. This can be moved by rain water, wind, ice, or gravity.

Need more help? eschooltoday – Rocks Kahn Academy - Three kinds of rocks video.