Transcript Slide 1
8th grade science Vocabulary texture – look and feel of rock’s surface grains – particles of minerals or other rocks in a rock extrusive – rock formed from lava cooled on Earth’s surface intrusive – rock formed from magma hardened beneath Earth’s surface sediment – small, solid particles from other rocks or material deposition – settling of sediment out of water or wind compaction – pressing of sediment together cementation – process in which dissolved minerals crystallize and glue sediment together Vocabulary cont. atoll –ring-shaped coral island found far from land foliated – when rock grains are arranged in parallel layers or bands metamorphic igneous sedimentary Classifying Rocks Need to observe rock’s color and texture to determine mineral composition Color alone will not be enough- need to look at how rock looks and feels Most rocks made up of particles of minerals or other rocks which is texture Texture is determined by grain: grain size - can be large (coarse grained) or small (fine grained) grain shape – have a wide variety, is result from shape of crystal forming rock grain pattern – will often have a pattern, flat layers, wavy swirling, or random no grain – may have no crystal grain noticeable due to quick cooling Often mineral composition looked at under microscope Rock put in one of three major groups: igneous sedimentary metamorphic Igneous Rocks Are classified by origin, texture, mineral composition Origin means where rock formed – above ground (extrusive) or below ground (intrusive) Texture will depend on crystal size which depends on amount of time rock took to cool Some rocks will have both large and small crystals as a background Rock is then said to have a porphyritic texture Mineral composition is affected by amount of silica in lava Magma with high silica content usually will form light colored rocks Metamorphic Rocks Is rock that has changed its form Heat and pressure deep inside Earth can change any rock into a metamorphic one Are classified by arrangement of grains making up that rock When grains are arranged in parallel layers or bands rock is said to be foliated and will split along the layers Some are nonfoliated – grains are arranged in random pattern and these will not split into layers Foliated Nonfoliated Sedimentary Rocks Sedimentary rocks form from sediment from material that has been eroded away by water or wind and then deposited somewhere else Over millions of years the deposits build up and are squeezed tightly together from weight of the build up While compaction is taking place the minerals dissolve in water which crystallizes and glues the particles together Type of sedimentary rock is based on the make-up of the rock: clastic rock – formed when rock fragments are squeezed together organic rock – formed from remains of plants and animals deposited in thick layers chemical rock – formed when minerals dissolved in a solution crystallize Reefs Best known sedimentary rock are coral reefs or atolls found in the ocean Coral reefs are the build up of skeletons of coral animals Three types of coral reefs: fringing reefs barrier reefs atolls Fringing reef Barrier reef Atoll Lab - Rock Cycle Question: How does a rock change in the rock cyle? Hypothesis: Materials: crayons of 3 different colors pencil sharpener aluminum foil piece of wood hot plate tongs tin can pan Procedure: 1. The crayons represent a rock. Take your “rock” and shave it on the aluminum foil so that you have 3 layers of “deposits”. 2. Now fold the aluminum foil over the “deposits” and place the piece of wood on top. Press down applying pressure to the “deposits” below. 3. Next fill the can with cold water. Place the aluminum Lab 12 The Rock Cycle continued packet on the hot plate and melt the “rock”. Once the “rock” is melted use the tongs to pick up the packet and place it in the water in the tin can. This should quickly harden the liquid “rock”. 4. Once the “rock” has hardened peel away the foil and view the results. Results: Conclusion: 1. What part of the rock cycle do the shavings represent? 2. When you put the wood on top of the packet and pressed down what happened to the shavings? What part of the rock cycle did that represent? 3. What did the heating of the packet represent? 4. What does the hardening represent? 5. How is this rock cycle different from the real one?