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 When studying a rock sample, geologists observe three things:  Mineral Composition  Color  Texture.

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Presentation on theme: " When studying a rock sample, geologists observe three things:  Mineral Composition  Color  Texture."— Presentation transcript:

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2  When studying a rock sample, geologists observe three things:  Mineral Composition  Color  Texture

3  Rocks are made of minerals and other materials.  Some rocks contain only one mineral. Others can contain many different types of minerals.

4  There are about 20 minerals that make up most rocks.  These minerals are known as rock-forming minerals.

5  Geologists look at the shape and color of the mineral crystals in the rock to help identify what the minerals are.

6  A rock’s color can help geologists know what minerals are in it.  For example, when we were studying volcanoes, we know that magma with more silica was lighter in color. The same is true of rocks with more silica.

7  A rock’s texture is a very useful way to identify the rock.  A rock’s texture is the look and feel of the rock’s surface.  Some are smooth and glassy.  Some are rough or chalky.

8  Most rock’s are made up of particles of minerals or other rocks called grains.  Grains give the rock its texture.

9  To describe a rock’s texture, geologists use:  Size of grains  Shape of grains  Pattern of grains

10  If grains are large and easy to see, they are said to be coarse-grained.  If the grains are so small they need a microscope to be seen, they are said to be fine-grained.  Some rocks do not have any visible grains even under a microscope.

11  Some rocks have grains that have very smooth, rounded shapes.  Some rocks have grains with very jagged, sharp shapes.  Some rocks have grains that are rounded AND grains that are jagged.

12  The grains in rocks can form different patterns.  Sometimes the grains form flat layers.  Sometimes they occur randomly.  Sometimes they form swirling patterns.

13  Igneous rock forms from magma and lava hardening back into a solid.  The name igneous comes from the Latin word ignis, meaning “fire”.  This is also where we get the word ignite from.

14  Igneous rocks are classified according to three things:  Origin  Texture  Mineral Composition

15  Igneous rock can form either on Earth’s crust, or under Earth’s surface.  Extrusive rock is formed from lava that has erupted and cools when it is outside of the volcano and on Earth’s surface.  Intrusive rock forms when magma hardens beneath Earth’s surface.

16  Lava that cools quickly forms very fine- grained igneous rocks with small mineral crystals.  There will be small to no visible grains in the rock.

17  Slow-cooling magma will form coarse- grained rocks with large mineral crystals.  The rocks will have large, easy to see grains.  Intrusive rocks have larger crystals than extrusive rocks.

18  Remember that different types of lava have different amounts of silica.  Minerals in rock that have a lot of silica will be very lightly colored and minerals that have less silica will be darker.  Rocks with more silica will be lighter in color than rocks with less silica.

19  Sedimentary rocks form over millions of years as particles of mud, sand, and volcanic ash are deposited and compacted and become solid rock.

20  Most sedimentary rocks are formed through a series of processes.  Erosion  Deposition  Compaction  Cementation

21  Destructive forces are constantly breaking up and wearing away the rocks on Earth’s surface.  These forces include heat and cold, rain, waves, and grinding ice.

22  In erosion, running water, wind, or ice loosen and carry away fragments of rock.  These fragments of rock are called sediments. ▪ Sediments are also particles of shells, bones, leaves, stems, and remains of other living things.

23  The sediments that were moved by the running water, wind, or ice will eventually sink to the bottom of the water or be dropped by the wind or ice.  Deposition is the process where sediments settle out of water or wind.  The particles of rock are now laying on the earth.

24  The process that presses sediments together is called compaction.  Thick layers of sediments builds up over millions of years.  The new layers push down on the older, lower layers, squishing them together tightly.

25  During compaction, the minerals in the sediments dissolve into water.  Cementation is when the dissolved minerals recrystallize and act as a glue holding all of the sediment together.

26  Geologists classify sedimentary rocks based on the sediments that are in the rock.  There are three major types of sedimentary rock:  Clastic  Organic  Chemical

27  Clastic  A clastic rock is a sedimentary rock that forms from rock fragments that have been squeezed together and cemented.  Most sedimentary rocks are clastic.  Clastic rocks are further classified based on the size of the rock fragments (grains).

28  Organic  Not all sedimentary rocks form from particles of other rocks.  Organic rocks form from the remains of plants and animals.  The term “organic” means that the substances were once part of living things.

29  Chemical  When minerals that are dissolved in a solution crystallize, chemical rock forms.

30  Metamorphic rocks are rocks that have changed form.  Any type of rock can change into metamorphic rock. (Igneous, sedimentary, or metamorphic)  Meta means “change”.  Morphosis means “form”.

31  Rock can change form when one or both of the following things are applied to it:  Heat  Pressure

32  Collisions between plates pushes rock downwards.  This adds pressure from the crust of the Earth and heat from the mantle, causing the minerals to change into other minerals, forming metamorphic rock.

33  When rock changes into metamorphic rock, its appearance, texture, crystal structure, and mineral content change.

34  Geologists classify metamorphic rocks according to the arrangement of the grains that make up the rocks.  There are two main types of metamorphic rock:  Foliated  Nonfoliated

35  Foliated  Metamorphic rocks that have their grains arranged in parallel layers or bands are said to be foliated.

36  Nonfoliated  Some metamorphic rocks are nonfoliated.  The mineral grains in these rocks are arranged randomly.


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