CHAPTER 19UNIT 5

ROCKS AND MINERALS

The world formed from Stardust

We formed from the world

We all came from Rocks

So now Mrs Stanford is calling us

Nuclear waste and Rock-heads

19.5 OBJECTIVESDescribe the three major types of

rocks and how they formDiscuss physical and chemical

properties of each major type of rock

Describe the rock cycleExplain how to find relative rock

ages and absolute rock ages

SOME INTERESTING FACTSDiamond, the hardest mineral on

earth, is composed of Carbon. The same material needed for life as we know it.

Most of the earth’s crust is made of some form of quartz

Diamonds, Rubies, Quartz, Garnets, and most of the precious gems we are familiar with come in many colors

THE COLORS OF FIREWORKS COME FROM DIFFERENT MINERALS

Magnesium burns white and very hot (don’t believe me, burn an old VW Bug engine in a bonfire)

Copper burns green (copper is also toxic, many gem cutters don’t work with Malachite, which is a semi-precious gemstone containing copper)

MINERALS AREA natural, inorganic solid with a

definite chemical composition and a characteristic internal structure

Ex. Quartz, is silicon dioxide, SiO2

THE STRUCTURE OF QUARTZ

Think of Triangular Pyramids being put together a specific way, over and over and over

THE MINERAL QUARTZ

MOST ROCKS ARE A COMBINATION OF SEVERAL MINERALS

Granite is a rock composed of different minerals

Coal is decomposed plant matter

NINE MOST COMMON ROCK-FORMING MINERALS

Feldspar

Pyroxene

Mica

Clay

Calcite

Quartz

Olivine

Dolomite

Amphibole

THE APPEARANCE OF ROCKSAppearance and Characteristics

reflect mineral composition (what is it) and the way it was formed

There are three major types of rocks – Igneous

Sedimentary Metamorphic

IGNEOUS ROCKS FORM FROM LIQUID ROCK

Remember the difference between Magma and Lava

Magma is underground

Lava is on the surface

BOTH ARE FORMED FROM

VOLCANOES

Granite forms from magma

Granite cools underground,

Granite is courseYou can see

different grains

Obsidian forms from lava

Cools quickly on the surface

Obsidian is smooth like glass

Obsidian you can’t see grains

Granite is an Intrusive Igneous Rock

Obsidian is an Extrusive igneous rock

SEDIMENTARY ROCKS

Rocks are not permanent structures, they break down by a process called

Weathering Weathering changes the

physical form or chemical composition of rock minerals exposed at earth’s surface

Weathering can be from wind, rain, acids…

SEDIMENTARY ROCK

Making new rock from old weathered rock Rock formed from compressed or cemented

deposits of Sediment Sediment is weathered rock, carried away by

wind or water and deposited in an new location

Sediments can be deposited by rivers, wind (sand dunes), glaciers, oceans…

FOSSILS Sedimentary rock often includes the

bodies or remains of animals and plants

Dinosaur National Monument, in North-West corner of Colorado is a large sedimentary rock formation that has been exposed by humans to uncover the remains of many dinosaurs

DINOSAUR NATIONAL MONUMENTQUARRY VISITOR’S CENTER

TWO WAYS TO FORM SEDIMENTARY ROCK

Pressure – rocks and water above can squeeze sediments into sedimentary rock

“Glue” – rocks dissolve and enter pores and resolidify gluing the sediments together

SOME TYPES OF SEDIMENTARY ROCKS Conglomerate – made of

pebbles and large visible rocks cemented together with a brown material of mostly quartz

Sandstone Mudstone, if flaky called Shale Limestone – made of fossils of organisms

that lived in water

LIMESTONE

Forms Caves Limestone dissolves

in water and leaves a cavity in the ground

Some minerals that are already in the water deposit in the cave leaving formations

STALAGMITES AND STALACTITES

Some amazing

formations found in

caves

METAMORPHIC ROCKS“TO CHANGE FORM”Rocks that started as

Igneous or Sedimentary can be changed by “squeezing”, “heating” or sometimes a chemical process

Usually both heat and pressure are involved in metamorphosing a rock

LIMESTONE (SEDIMENTARY) BECOMES MARBLE (METAMORPHIC)

Heat and pressure turn limestone into marble

Marble will often have bands of color and swirls

MARBLE, COLORADOUSED IN MONUMENTS IN WASHINGTON DC

MARBLE USED IN SCULPTURE

SLATE Shale (remember that’s flaky mudstone) turns

into slate when heated and compressed Shale and slate are often rock types where oil

and natural gas can be found Geologists searching for gas and crude oil

look for evidence of these rocks

THE ROCK CYCLE

http://www.classzone.com/books/earth_science/terc/content/investigations/es0602/es0602page02.cfm

HOW OLD ARE ROCKS? Can be hard to tell We can find relative

age using “Law of Superposition”

Older rocks are on the bottom,

Examples Grand Canyon, Layers of rocks seen in Grand Junction Area…

Fossils in rocks lower in a rock face are older than fossils in rocks above them

TO FIND THE ACTUAL AGE WE NEED SOMETHING DIFFERENT -

RADIOACTIVE DATING Radioactive elements will “decay”

- they break down to other elements or forms Carbon, Argon, Rubidium, Strontium, Uranium

and Lead are all used for Radioactive Dating Determines absolute age of rock

Rocks in Minnesota are 3.2 billion years old Rocks in Greenland are 4.2 billion years old