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Types of rocks
- 2. What is aRock? • Naturally-occurring mixtures of minerals, mineraloids, glass or organic matter.
- 3. What is aRock? • Rocks are divided into 3 groups based on how they were formed: •IGNEOUS •SEDIMENTARY •METAMORPHIC
- 4. What is thedifference between a rock and a mineral? • Rocks are made up of ONE or MORE minerals.
- 5. Once a rockis formed, does it stay the same rock forever? • NO!
- 6. • Rocks arecontinually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling • Rocks can change to and from the three types
- 7. What is theprocess through which rocks change? • The Rock Cycle—earth materials change back and forth among the different types of rocks
- 9. • No setpath a rock takes to become another kind of rock
- 10. • “Ignis” =Latin for “fire” • Formed from the cooling of either magma or lava • The most abundant type of rock • Classified according to their origin and composition
- 11. ORIGIN— Where rocksare formed • Below ground = from magma (intrusive igneous rock) • Usually have LARGE crystal grains (they cooled slowly)
- 12. Some have large& small crystals (called porphyritic)
- 13. • Above ground= from lava (extrusive igneous rock) • Usually have SMALL or NO crystals (they cooled too quickly)
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- 18. COMPOSITION— What kindof substances the rocks are made of
- 19. Basaltic Igneous Rocks—made from lava/magma that is low in silica, rich in iron and magnesium. Rocks are dark-colored.
- 20. Granitic Igneous Rocks— madefrom magma/lava high in silica and oxygen. Rocks are light-colored.
- 21. Andesitic Igneous Rocks— havea composition between basaltic and granitic.
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- 25. • Formed fromsediments (rock fragments, mineral grains, animal & plant remains) that are pressed or cemented together or when sediments precipitate out of a solution.
- 26. • These sedimentsare moved by wind, water, ice or gravity. • Sedimentary rocks represent 7% of the Earth’s crust, but they cover 70% of the Earth’s surface. • Sedimentary rocks are fossil-carrying rocks.
- 27. What turns sedimentsinto solid rock? • Water or wind breaks down and deposits sediment (erosion & deposition)
- 28. • The heavysediments press down on the layers beneath (compaction)
- 29. • Dissolved mineralsflow between the particles and cement them together (cementation)
- 30. How can sedimentarylayers help us understand the age of fossils? • As sedimentary rocks are deposited, they form horizontal layers • Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.
- 31. 3 Types ofSedimentary Rocks: • Clastic (also called Detrial)—made of broken pieces of other rocks
- 32. Organic—remains of plantsand animals are deposited in thick layers • Examples • Fossil rich limestone is made from the shells of ocean animals; used to make chalk 3 Types of Sedimentary Rocks:
- 33. • Chemical—minerals dissolvedin lakes, seas, or underground water 3 Types of Sedimentary Rocks: Mineral crystals are made as the shallow water that has flooded the bottom of Death Valley evaporates. Click on image for full size (66K JPG) Courtesy of Martin Miller, University of Oregon
- 34. Examples • Limestone made when calcite mineral precipitates fromsea water • Rock Salt— made from evaporation of sea waters
- 35. • Rocks thathave changed due to intense temperature and pressure • “Meta” means “change” and morphosis means “form” in Greek • Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks
- 36. What occurs inthe Earth to change these rocks? • Pressure from overlying rock layers • High heat, but not enough to melt the rock • Rocks may be flattened or bent or atoms may be exchanged to form new minerals.
- 37. How are metamorphicrocks classified? • Foliated—mineral grains are flattened and line up in parallel bands • Example: gneiss formed from rearrangement of minerals in granite into bands
- 38. How are metamorphicrocks classified? • Non-Foliated—No bands are formed • Example: marble formed from limestone
- 39. Where do metamorphicrocks usually form? • Where magma intrudes relatively cool rock • Near colliding plates (near mountain ranges) • Places that are covered miles thick with other rock causing pressure • When hot water intrudes rock • Where a meteorite strikes Earth (rare) • Where lightning bolts strike rocks (rare)