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Rocks chapter 3.

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Presentation on theme: "Rocks chapter 3."— Presentation transcript:

1 Rocks chapter 3

2 The Rock Cycle section 1 What is a rock?
Common rocks: rock is a mixture of minerals, rock fragments, volcanic glass, organic matter and other natural materials

3 Rock Cycle Rock cycle illustrates the processes that create and change rocks Rock interchange between igneous, sedimentary and metamorphic rock depending how they form , the process it takes to form new rock and may take millions of years to form When matter weathers it is not lost but arranged in perhaps different forms

4 Igneous Rock section 2 Formation of Igneous Rock: Hot magma cools and solidifies to form igneous rock Magma: the decay of radioactive elements deep in earth interior and intense pressure cause rocks below 150 km to melt. That melted rock is called magma Magma is less dense and rises to surface. When it reaches the surface it is called lava

5 Intrusive rock Rock that cools underneath the surface is intrusive rock Cooling is slower and slower than rock that reaches the surface The slower rock cools the larger the crystal form (coarse grained)

6 Extrusive Rock Magma cools at the surface and is called extrusive rock
Crystals do not have time to form generally (fine grained)

7 Volcanic Glass Pumice, obsidian and scoria are examples of volcanic glass These cool so fast that few or no mineral grains form Gas is trapped in mineral leading to pockets of gas trapped in mineral

8 Classifying Igneous Rock
Basaltic Rock: rock rich in iron, dark, dense, poor in silica(SiO2) (basalt is an example) Granitic rock; rich in silica, light colored, lower density: builds up pressure before released. Usually cools before it reaches the surface (granite is example) Andesitic Rock: composition between basaltic and granitic rock (Cascade Mt are example)

9 Metamorphic rock section 3
Metamorphic rock is changed rock caused by intense pressure and temperature deep under earths surface Can form from a parent material of igneous or sedimentary rock or metamorphic rock Shale can change to slate Slate into schist, and eventually to gneiss

10 Classifying Metamorphic Rock
Foliated rocks: when mineral grains line up in parallel layers, it is said to have metamorphic foliated texture Slate: watertight metamorphic rock caused by pressure is used in pools and roofs Gneiss: forms when granite is put under intense pressure and give layers of light and dark areas

11 Nonfoliated Rocks Metamorphic rock where layering doesn’t form but form rearrange layers are nonfoliated rocks Sandstone is sedimentary rock that when heated and under lots of pressure form quartzite with interlocking quartz in between Marble: composed of mineral calcite (limestone), that has under gone intense pressure and temperature

12 Sedimentary Rock section 4
Formation of Sedimentary Rock 75 % of rocks exposed at the surface are sedimentary rocks Sediments are loose materials ie rock fragments, minerals grains, bits of shell moved by wind water, ice, or gravity Sedimentary rocks forms when sediments are pressed and cemented together or when minerals form from solution

13 Stacked Rocks Rocks that are deposited in layers usually hold the rocks at the bottom of layers are older and younger rocks rest on top On occasions, the layers get messed up and the age of the rocks don’t hold true to the layers

14 Classifying Sedimentary Rocks
Classified by being either detrital, chemical or organic Detrital: sedimentary rock made from the broken fragments of other rock which are compacted and cemented together Rock first must be broken down or weathered and then moved to another location by erosion Compaction of smaller particles can stick together to form solid rock under pressure

15 Detrital Sedimentary rock
Cementation: larger sediment (pebbles and sand) with only pressure can’t bind together, but rather need cementation to hold rock together Water mixed with dissolved material acts as a cement to hold larger particles together Shape and size of sediment are given names Conglomerate (rounded pieces of pebbles cemented together Breccia are sharp jagged pieces cemented together

16 Materials found in Sedimetnary Rocks
Can be chunks of minerals, (quartz,feldspar) pieces of gneiss, granite, limestone The cement usually made up of quartz or calcite Sandstone is formed from smaller particles Sand size particles usually quartz and feldspar Siltstone: similar to sandstone except granules are smaller Shale: particles made from clay sized particles

17 Chemical Sedimentary Rock
These rocks are not made from pre-existing rock These rocks form when dissolved minerals come out of solution When evaporation takes place in a solution of minerals, they will drop out of solution Gypsum: rock from New Mexico Limestone: Calcium carbonate carried to ocean in solution and comes out of solution in form of calcite (usually deposited in shallow lakes)

18 Chemical sedimentary rocks
Rock salt: halite forms from salt (NaCl) that evaporates out of solution and forms cubic crystals

19 Organic Sedimentary Rocks
Rock forms from the once living remains Most common is fossil-rich limestone Formed from once living ocean organisms instead of just calcite deposits Shells of marine organism are made of CaCO3 that eventually becomes calcite where they are cemented together Coquina : rock made of shell fragments

20 Organic Sedimentary Rocks
Chalk: calcite-shell remains of once living ocean organisms Coal: dead plants are buried under other sediment in swamps Plants become chemical changed by organisms United States has a lot of coal produced in Carboniferous period ( million ya)

21 Another look at Rock cycle
Rock cycle has no beginning or end Rocks formed can be uplifted, weathered, eroded, buried, cemented, melted, more pressure, uplift continuously

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