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Metamorphic Rocks.

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Presentation on theme: "Metamorphic Rocks."— Presentation transcript:

1 Metamorphic Rocks

2 Metamorphic Rocks produced from preexisting igneous, sedimentary, or from other metamorphic rocks (called parent rock) Metamorphism means to “change form” leads to changes in the mineralogy, texture, and sometimes the chemical composition of rocks.

3 Recrystallized Minerals Can Be More Stable

4 Metamorphic Rocks Causes include changes in temperature, pressure (stress), and the introduction to chemically active fluids. Heat is the most important of metamorphism because it provides the energy to drive chemical reactions that result in the recrystallization of existing materials and/or the formation of new materials. Earth’s internal heat comes mainly from radioactive decay within the Earth’s interior.

5 Metamorphic Rocks 2. Pressure, like temperature, increases as you get deeper into the Earth. Buried rocks are subjected to: Confining pressure – equal squeezing and minerals closer together; dense Differential pressure – unequal squeezing and develops folds or foliation


7 Metamorphic Rocks 3. Chemically active fluids
the circulation of hot, mineral-laden fluids through rock bodies

8 Metamorphic Rocks

9 Metamorphic Rocks slight changes (low-grade metamorphism) shale turning into slate because of not terribly high pressures or temperatures. Fine grained substantial changes (high-grade metamorphism). Slight melting may occur, as well as folds or obliteration of fossils in the parent rock. Coarse grained

10 Examples of Metamorphic Rocks
Quartzite Slate Gneiss Marble Phyllite Schist

11 Metamorphic Rock Textures
Texture is used to describe the size, shape, and arrangement of grains within a rock. 2 types: Foliated Non-foliated quartzite

12 Examples of Foliated Textures
Schist has minerals (such as mica) that have grown large enough to be seen by the unaided eye Slate is a rock with excellent rock cleavage, as it breaks in flat slabs. Gneiss results from high-grade metamorphism

13 Foliated Metamorphic Rocks
Slate Gneiss Schist Phyllite

14 Nonfoliated Metamorphic Texture
Marble (Parent rock of Limestone) Porphyroblasts are large grains that are surrounded by a fine-grains of other minerals. GARNETS Quartzite (Parent rock of sandstone)


16 The exterior of the Taj Mahal is constructed mainly of the metamorphic rock marble.

17 Metamorphic Environments
Hydrothermal metamorphism occurs when hot fluids circulate through fissures and cracks that develop in rock. This hot fluid chemically alters rocks and is closely related to igneous activity.

18 Metamorphic Environments
There are a number of environments in which metamorphism occurs. Most are in the vicinity of plate margins, and many are associated with igneous activity. Contact or thermal metamorphism occurs when rocks immediately surrounding a molten igneous body are “baked” and therefore altered from their original state.

19 Metamorphic Environments
Regional metamorphism occurs where rocks are squeezed between two converging lithospheric plates during mountain building.

20 Igneous Rocks Igneous rock forms when magma cools and makes crystals.
Magma is a hot liquid made of melted minerals. When magma pours onto the earth’s surface it is called lava. The minerals can form crystals when they cool. Fast cooling results in small crystals. Igneous rock can form underground, where the magma cools slowly and results in large crystals. Or, igneous rock can form above ground, where the magma cools quickly. The crystals grow together and form one igneous rocks.

21 What kind of igneous rocks form when molten lava cools and hardens?
Extrusive Extrusive = forced out while molten through cracks in the earth's surface

22 What is the Latin word that the word igneous comes from and what does it mean?
ignis = fire

23 Extrusive Igneous Rocks
Formed by lava on the Earth’s surface

24 Intrusive Igneous Rocks
Form from magma below the earth’s surface

25 What is the difference between magma and lava?
Lava = molten rock flowing on the earth’s surface Magma = molten rock below the earth’s surface

26 Silicon, oxygen, aluminum, iron, calcium, sodium, potassium, magnesium
What are the 8 elements that make up magma? Silicon, oxygen, aluminum, iron, calcium, sodium, potassium, magnesium Basaltic rocks are low in silica. They are dark colored and dense. Basaltic rock is called “MAFIC” Granitic rocks have high silica content, are light in color, and have lower densities. Granitic rock is called “FELSIC”

27 In what ways are the two rocks similar?
Look at the granite rock and the rhyolite rock Granite Rhyolite In what ways are the two rocks similar? Both are from melted rock Their composition is the same – quartz and feldspar

28 In what ways are the two rocks different?
Granite Rhyolite Granite – coarse texture, made from magma Rhyolite – fine texture, made from lava

29 What causes the two rocks to be different?
Granite Rhyolite Granite – Slow cooling below the earth’s surface Rhyolite – Quick cooling on the earth’s surface

30 Why do you think some rocks are heavier than others?
Some are denser – less air space between particles

31 Which rock would have greater density?
Pumice Granite

32 Which is EXTRUSIVE? Andesite Pegmatite

33 Gabbro Basalt These 2 are related. They form the oceanic crust. Which one is most likely on the surface of the crust? Are they mafic or felsic?

34 Pumice Obsidian Both Pumice and Obsidian are extrusive. Why don’t they exhibit crystalline structure? The pumice has “vesicles” like a slice of bread. How do those form? Which one has such low density that it floats in water?

35 Slow cooling magma will form rocks with a
a. coarse grained texture. b. fine grained texture. c. glassy texture. d. porphyritic texture.

36 Rapid cooling magma will form rocks with a
a. coarse grained texture. b. fine grained texture. c. glassy texture. d. porphyritic texture.

37 Imagine magma cooling slowly, deep in Earth’s crust
Imagine magma cooling slowly, deep in Earth’s crust. Suddenly, it is moved higher in the crust and some erupts onto the surface. What type of texture would result? a. coarse grained texture. b. fine grained texture. c. glassy texture. d. porphyritic texture.

38 Bet Cha’ Weren’t Expecting A…. POP QUIZ!!!!!*
What are the three types of rock? Which type of rock has been formed by magma or lava? What do we classify rocks by? How do sedimentary rocks form (in order)? Metamorphic rocks are rocks that have ?(fill in the blank) What is the process of sediments forming a sedimentary rock? What does “ignis” mean in the word igneous? *Answers are on next slide!

39 ANSWERS!!!! Igneous, Sedimentary, and Metamorphic Igneous
Texture, Color, and Mineral Composition Erosion, Deposition, Compaction, Cementation Morphed Lithification “ignis” means fire

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