Rocks

Classified based on their origin (How they formed).

IgneousSedimentaryMetamorphic

IGNEOUS

These rocks used to be magma!Born of fire!Molten rock (magma) solidifies as it

cools allowing crystals to form.There are two types:

Extrusive igneous rock!Intrusive igneous rock!

Extrusive Igneous Rocks (Volcanic)

Form near or at the earth’s surfaceComposed of small crystals

(Texture)Not enough time for crystals to

grow large!Rapid crystal growth due to rapid

loss of heat!

Intrusive Igneous Rocks (Plutonic)Form deep under earth’s surfaceComposed of Large crystals

(Texture)Lots of time for crystals to grow

large!Slow crystal growth due to slow

loss of heat!

Naming Igneous Rocks

Use the ESRTCross reference (for each sample):Texture/Grain sizeColorDensityComposition

Distinguishing Characteristics

Look for scattered crystals!Shiny/glassy looking bits all

locked together…Vesicularity (air pockets)NOT ARRANGED IN LAYERS

Sedimentary Rocks

These rocks used to be sediments!Generally form in still water!There are three types:ClasticChemical (crystalline or evaporites)Bioclastic

Clastic Sedimentary Rock

Sediments-Small bits of weathered rock are deposited (layed down in layers)

Layers become compressedSediment is cemented together by

mineral deposits between grains.

Where sediments accumulate:

a- alluvial fans j- continental shelf

b- Glaciers k-continental slope

c- rivers l-abyss

d- dunes m-reefs

e- lakes

f- lagoons

g- esturies

h-deltas

i- tidal flats

Chemical/Evaporites

Form as mineral rich water evaporates.

Mineral solidifies as water evaporates and settles out as an evaporite deposit!

Organic/Bioclastic

Form either directly or indirectly from living things.

Coal - Formed as trees and plants decayed over millions of years in swampy areas!!

Limestone - shells and other aquatic wastes combine in layers!

Distinguishing Characteristics

Sedimentary rocks exhibit one or more of these:

Layers of sediments (usually horizontal).

Fossils in the rock!Earthy (dull) color.Composed of sediments..NOT

crystals!

Naming Sedimentary Rocks

USE THE ESRTCross reference your observations with chart on pg.7

Environment of formation inferences!

Large sediments indicate fast water during deposition (shallow, near shore environment).

Small sediments indicate slow water during deposition (deep water environment).

Types of fossils (Land or aquatic environment based on organism).

Metamorphic Rocks (Changed Rocks)

These used to be other rocks!Formed by heat and/or

pressure within the crust!Rocks re-crystallize without

melting!

Types of Metamorphism

Regional – Pressure is the dominant process causing change in rock!

Large areas deep within the earth in areas of mountain building!

Revealed over millions of years by weathering and erosion!

Contact– Heat is the dominant process causing change!!

Small areas within the crust where magma is injected!

Magma cools but is still hot enough to cause change of the surrounding rock!

MAGMA DOES NOT MELT ROCK

Distinguishing Characteristics

Increased densityPressure squeezes the atoms of the rock closer together…Decreasing the volume without changing the mass!

Foliation

Crystal growth in the direction of pressure…

Causes layers of crystals along which the rock may break…

Much like cleavage in minerals!

Banding

Increased pressures cause new minerals to form with different colors

Appears as alternating dark to light bands around rock!!

Distortion

Twisting of the rock structure due to increased pressure

Rock cycle

Over time ALL rocks can change into any other kind of rock as their environment changes!

Follow the arrows through the Rock Cycle Chart (ESRT).

The process causing change is on the arrow!