RocksRocks

IgneousMetamorphicSedimentary

What is a Rock?

• A rock is composed of minerals

• Can be made of organic material

• Solid material that forms Earth’s hard surface.

Igneous RockIgneous Rock

Igneous Rock

• Rock that crystallizes from cooling of magma (inside Earth) or lava (on/outside surface of Earth)

• Characterized two ways – INtrusive or Extrusive

• Geology Kitchen Video - Igneous Rocks

• Crystallizes inside of Earth from magma

• Magma cools slowly (because of the blanket of the Earth’s layers)

IntrusiveIntrusive Igneous Rock Igneous Rock

Intrusive Igneous Rock (continued)

• Cooling slowly = large interlocking crystals (usually two or more colors)

• Large crystals = coarse-grained texture

Devils Tower, Wyoming

Igneous Intrusive Rock Samples

GraniteGranite

Note 3 minerals = mica (black)Note 3 minerals = mica (black)quartz (smoky)quartz (smoky)feldspar (pinkfeldspar (pink))

ExtrusiveExtrusive Igneous Rock Igneous Rock

• Crystallizes outside of Earth from lava – mostly from volcanic activity

• Lava cools quickly• Cooling quickly = tiny or no

mineral grains (usually one drab color)

Extrusive Igneous Rocks (Continued)

• Tiny or no mineral grains = fine-grained texture

• EXTRA : Sometimes has pores or holes from trapped gases

Extrusive Igneous Rock Samples

PumicePumice

Basalt (seafloor)Basalt (seafloor)

ObsidianObsidian (volcanic glass)(volcanic glass)

Notice the very smooth texture

Notice the drab colorNotice the holes or pores

MaficMafic vsvs FelsicFelsic

• Mafic igneous rocks - dark in color and have a high density due to high quantities of heavy elements (magnesium, iron, calcium and sodium)– basalt (extrusive) and gabbro (intrusive).

• Felsic igneous rocks – light in color and have a lower density due to high quantities of lighter elements (silicon, oxygen, aluminum, sodium and potassium)– Pumice (extrusive) and granite (intrusive)

Sedimentary Rock

• How does Sedimentary Rock form? • Click on image for video clip

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Sedimentary RockSedimentary Rock• Formed at surface of Earth (in lakes,

oceans, rivers) in thin or thick layers (strata)

• Layering is referred to as stratification• Formed from Cementation & Compaction

of sediments or Evaporation/Precipitation• Only rock type to contain fossils – one

exception = volcanic ash• Characterized two ways – clastic or non-

clastic

Sedimentary Rock Strata

ClasticClastic Sedimentary Rock Sedimentary Rock

• Mineral grains (sediments/fragments) are compacted and cemented together.

• Example – sand compacted and cemented = sandstone

• Example – mud/clay compacted and cemented = shale

• Example – pebbles, sand and mud compacted and cemented = conglomerate

• Geology Kitchen Video – Clastic Sedimentary Rock

ClasticClastic Sedimentary Rock Sedimentary Rock SamplesSamples

sandstonesandstone

shale fieldshale field

Non-clasticNon-clastic Sedimentary Sedimentary RockRock

• Two types – Organic Non-clastic or Chemical Non-clastic

• Organic – made from once living things – plants (coal) or animal life (fossil rich limestone - coquina)

• Chemical – made from evaporation (gypsum) or precipitation – (CaCO3 – chemical limestone)

• Geology Kitchen Video – Chemical and Biologic Sedimentary Rock

Non-clastic Sedimentary Rock Samples

Coal - organicCoal - organic

Fossil rich limestone - organicFossil rich limestone - organic

Chemical limestoneChemical limestone

Gypsum - chemicalGypsum - chemical

Sedimentary Features

• Ripple Marks – left by water or wind in sand, mud, etc. – can be preserved as a rock feature

Sedimentary Features

• Mud cracks in today’s puddles can be preserved as rock millions of years from now

Sedimentary Features

• Cross bedding – formed in old sand dunes or on off-shore sand bars

Metamorphic RockMetamorphic Rock

• How is metamorphic rock formed?

Metamorphic RockMetamorphic Rock• Formed deep inside the Earth from

intense heat and pressure • Any rock type can be changed by

metamorphism – depends on how much heat, pressure and original rock type to determine the outcome

• No melting involved – solid state process (more like softening)

• Hardest of three types of rock• Characterized two ways – foliated or

non-foliated• Geology Kitchen Video - Metamorphism

FoliatedFoliated Metamorphic Metamorphic RockRock

• Banding (stripes) or cleavage (flaky) is present

• Always a change structure and texture of original rock and sometimes a change in the composition.

• When composition changes – most often a semi to precious gem can be formed.

• Animation of metamorphism forming foliated rock

• Generally created from a rock that had more than one color.

FoliatedFoliated Metamorphic Rock Metamorphic Rock SamplesSamples

schistschist

Gneiss (Previously granite)Gneiss (Previously granite)

Slate (previously shale)Slate (previously shale)

Non-foliatedNon-foliated Metamorphic Metamorphic RockRock

• NO Banding and/or NO cleavage

• Change in structure and texture of original rock

• Possible change in composition.

• Generally created from rocks with only one color

Non-foliatedNon-foliated Metamorphic Metamorphic Rock SamplesRock Samples

Quartzite Quartzite (previously sandstone)(previously sandstone)

Marble Marble (previously limestone)(previously limestone)