Ch. 4

 Believe it or not most monuments are made of rocks!  In fact these rocks contain minerals such as: quartz, feldspar, mica, or calcite  A rock is a mixture of The previous minerals

 The Rock Cycle explains how rocks slowly change through time (Pg. 92)  The rock can be transformed by Many processes:  weathering, erosion, deposition, heat, and pressure  However, these rocks change though matter is always conserved

 James Hutton: Scottish Physician (1788)  Noticed rocks undergo changes, but some rocks look like they are in layers - ex.) Siccar Point  After he discovered this he published a book and that book is still used today

 Many different ways…but really 3 main ideas  Igneous, Metamorphic, Sedimentary  However we first need to see 2 things:  Composition : what’s it made up of  Texture : What are the grain sizes?

 Formation is caused by volcanic eruptions or processes similar to it  When this volcanic material hardens we get igneous rocks!

 In certain parts of the Earth conditions are right to melt rock - Most magma comes from deep below Earth’s surface -When magma reaches Earth’s surface and flows it is called Lava

 When rocks are made below Earth’s surface from magma we call them intrusive rocks -takes a long time to cool, which leads to large crystal size -these create unique structures like batholiths and sills

 Form when lava cools on or near the Earth’s surface  This rock cools quickly, making really small crystal size

 Pumice, obsidian, and scoria  They cooled so quickly that there is no mineral size present  In the case of pumice, air gets trapped in the rock and causes the rock to become very light

 Are classified on how they are formed  Also can be tested on which magma they form from  These magma differences will lead to different -color -density -melting temperature

 Dense, Dark-colored rocks  Gabbro, Basalt  Are rich in Iron and Magnesium, which gives it a dark color  So why does the sand in Hawaii look so Dark?

 Are light-colored rocks  Ex.) Granite, Rhyolite  Lower density then Basaltic rocks  Rich and thick magma  Contain Calcium and Aluminum  Usually found with Volcanic eruptions

 Ever packed your lunch in the morning and then at lunchtime it is not recognizable?  This change can be from heat of your body next to it or the weight of everything in your backpack crushing it  These are similar to the processes that make metamorphic rocks

 These are rocks that have changed because of changes in temp. and pressure or presence of hot watery fluids  Can form from: -igneous -metamorphic -sedimentary

 Rocks beneath Earth’s surface are under an unreal amount of pressure  Temperature and Pressure increases as you go further underground  Under these conditions some minerals flatten out ( Regional Metamorphism -Earth contact)  Rocks melt and change do to Magma ( Contact Metamorphism )

 Each rock can be classified according to its composition and texture  We learn about 2 types: 1.) Foliated 2.) Non-foliated

 When mineral grains line up in parallel layers we call this foliated : banded texture  -Ex.) Slate and Gneiss 1.) Slate is formed from shale 2.) Gneiss is formed from granite ( not much changes except the alternating bands of light and dark rock)

 Minerals grains grow and rearrange but do not form layers: non-foliated  Ex.) Marble  Forms when sedimentary rock limestone rearranges and mixes with calcite  It does not form a banded layer though like slate or Gneiss

 Igneous are the most common rocks in the world  However, most occur below Earth’s surface  Sediments : loose materials such as rock fragments, mineral grains, and bits of plants and animal remains  Sedimentary rocks : rocks formed from pressed and cemented sediments

 Sedimentary rocs often form as layers  The older layers being at the bottom while the younger layers are on top  Think of the paper in your locker…  Sometimes Earth’s forces can disturb these layers and change their appearance  Fig. 11, pg. 103

 Can be made out of any material on Earth  These rocks are classified on their composition  We will learn about 3 types: 1.) Detrital 2.) chemical 3.) Organic

 Latin word meaning “wear away”  Table 2, pg 105 shows ex. of detrital rock

 When rocks are exposed to water or ice it breaks down  Both mechanically and chemically  This breaking down leads to the different sediment sizes (table 2)  Erosion: the movement of weathered material

 Erosion moves sediments to a new location where they are deposited  Here layers upon layers build up  The pressure from the upper surfaces pushes down on the rock below  This force can form rocks (this is called compaction)

 If sediments are large, like sand and pebbles, pressure alone can’t make them stick  Large pieces must be cemented together  Cementation occurs when water soaks into the soil, picks up atoms and molecules, and certain minerals then become deposited.  These minerals cement the rocks together  Pg. 105, fig. 13

 Detrital rocks have granular texture much like sugar  They are named according to shape and sizes of the sediments they form  Ex.) Conglomerate forms from large pebbles, also smooth round pebbles. If they were jagged it would be called Breccia

 These different materials found in different sedimentary rocks gives the rocks their unique characteristics and names  Siltstone: made of silt like particles  Sandstone: made of sand-sized particles  Shale: made of clay-sized particles

 Form when dissolved minerals come out of solution  Think of when H 2 O evaporating from Saltwater  These rocks are different because they are not made up of other rocks

 Calcium Carbonate is carried in solution in ocean water  When it evaporates it forms calcite and when these crystals form and grow it creates Limestone  Limestone is usually deposited on the bottom of lakes or shallow seas  DYK? Kansas has limestone beds. How?

 When water is think with dissolved salt it can form rock salt  When it evaporates it forms Halite  These can occur naturally from a few cm’s thick to over 400 m thick!

 These are rocks made of once-living things  One of the most abundant ones is Limestone  Limestone contains many, many fossils  Similar to chemical Limestone, organic limestone contains almost only fossils  Animals such as mussels, oysters, clams make shells from CaCO 3 (this is Calcite)  When the animals die and fall to the bottom they form limestone

 Chalk is another rock made of microscopic shells  When you use real chalk you are actually writing with crushed shells!

 Another useful organic rock  Coal forms when plants are buried under other sediments in swamps  These plants parts are chemically changed by microorganisms  The leftovers are compacted and under pressure for millions of years to form coal

 Most of the coal in North America formed during carboniferous period  It occurred~ million years ago  So much coal was formed then that it had a period in time named after it!

 The rock cycle has no beginning and it has no end  It is continuous!  Even the magma underground comes from rocks already existing  All rocks, even the ones used today, are part of the rock cycle  Slowly these rocks are even changing!!!