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 TAS-diagram for volcanicrocks

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Foliation Grain Size HardnessUsualColor

Other Rock Type

foliated ne soft dark"tink" whenstruck

Slate

foliated ne soft darkshiny;crinklyfoliation

Phyllite

foliated coarse hardmixed darkand light

wrinkledfoliation;often haslargecrystals

Schist

foliated coarse hard mixed banded neiss

foliated coarse hard mixeddistorted"melted"layers

!igmatite

foliated coarse hard dark

mostly

hornblende Amhibolite

nonfoliated ne soft greenishshiny#mottledsurface

Serentinite

nonfoliatedne orcoarse hard dark

dull andoa$ue

colors#found near

%ornfels

Identification of Metamorphic Rocks

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Hardness Grain Size Composition Other Rock Type

hard coarse clean $uart' white to brown Sandstone

hard coarse$uart' andfeldsar

usually verycoarse

Arkose

hard or soft mixedmixed sedimentwith rock grainsand clay

gray or dark and"dirty"

+acke,raywacke

hard or soft mixedmixed rocks andsediment

round rocks inner sedimentmatrix

onglomerate

hard orsoft

mixedmixed rocks andsediment

shar ieces inner sedimentmatrix

.reccia

hard nevery ne sand; noclay

feels gritty onteeth

Siltstone

hard ne chalcedonyno ''ing withacid

hert

soft ne clay minerals slits in layers Shale

soft ne carbonblack; burns withtarry smoke

oal

soft ne calcite ''es with acid /imestonesoft coarse or ne dolomite no ''ing with ac

id unless owdered0olomite rock

soft coarse fossil shells mostly ieces o$uina

very soft coarse halite salt taste 1ock Salt

very soft coarse gysum white# tan or ink 1ock ysum

Identification of Sedimentary Rocks

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Grain Size Usual Color Other Composition Rock Type

ne dark glassy aearance lava glass 2bsidian

ne light many small bubbleslava froth fromsticky lava

Pumice

ne dark many large bubbleslava froth from 3uidlava

Scoria

ne or mixed light contains $uart' high-silica lava 4elsite

ne or mixed mediumbetween felsite andbasalt

medium-silica lava Andesite

ne or mixed dark has no $uart' low-silica lava .asalt

mixed any colorlarge grains in ne-grained matrix

large grains offeldsar# $uart'#

yroxene or olivine

Porhyry

coarse lightwide range of colorand grain si'e

feldsar and $uart'with minor mica#amhibole oryroxene

ranite

coarse lightlike granite butwithout $uart'

feldsar with minormica# amhibole oryroxene

Syenite

coarse medium to dark little or no $uart' low-calciumlagioclase anddark minerals

0iorite

coarse medium to darkno $uart'; mayhave olivine

high-calciumlagioclase anddark minerals

abbro

coarse darkdense; always hasolivine

olivine withamhibole and,oryroxene

Peridotite

coarse dark densemostly yroxenewith olivine andam hibole

Pyroxenite

Identification of Igneous Rocks

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%ow To 8se The 9gneous 1ock 90

hart (age :) 

 The very rst thing tounderstand is thatyou must become

familiar with all thevocabulary on theage

 <ou need to know what thewords mean and you also needto remember where they are onthe chart so you can nd them$uickly and easily

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 The rst thing tounderstand is thatall of the names

in the uer(shaded) art ofthe chart are theigneous ROCKS. 9f you are askedfor the name of

an igneous rock #it must be one ofthese

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 The next thing tounderstand isthat all the names on thelower (shaded) art of thechart are the MINERALS that are commonly found inigneous rocks

 <ou should kee in mindthat since these areminerals# there is a lot ofinformation about each ofthem on age =: of yourreference tables

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9gneous rocks areclassiedaccording to twobasiccharacteristics>=) TEXTURE which is alsoknown as GRA!S"E

And

?) #ineralcomposition

+e need to be able touse these two characteristics in

order to identify one articular igneousrock

%ere@s how

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/et@s deal with the to art (IGNEOUS ROCKS) rst

All the igneous rocks are classied according to TEXTU

also called GRA! S"E

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Intrusive (Plutonic) rocks formed dee withinthe crust .ecause they were so dee theycooled very slowly giving the mineral crystals in

the rocks a very long time to grow That@s whyintrusive igneous rocks usually have a corseto ver! corse texture

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As you can see from the chart# coarse texture grain si'es of = to =6 mm and very coarse

texture grain si'es of =6mm and larger

ranite# 0iorite# abbro# Peridotite and 0uniteare the names of the corse "rine# i"neousrocks These rocks are !TRUS$E %&lutonic'rocks(

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Pegmatite is another !TRUS$E %&lutonic' igneous9t has very coarse texture with a grain si'e of =6mm olarger

  1&!&!.&1

!TRUS$E ) S*O+ COO*!G ) COARSE TEXTUR

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9gneous rocks with ne texture have grain si'es less than =mmrocks formed at or near the surface and are called EXTRUS$E%$olcanic' rocks

.ecause they formed at or near the surface they cooled raidlycrystals (grains) had very little time to grow so they remain small

1hyolite# Andesite# and .asalt are the ne grained igneous rocks

EXTRUS$E ) RA&, COO*!G ) F!E TEXTURE 

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Some EXTRUS$E %$olcanic' igneous rocks cool so fast that crcannot form Such rocks have no crystal structure (grain) and arclassied as G*ASS-  They are really volcanic glass

2bsidian# Pumice# and .asaltic lass are EXTRUS$E %.olcanicglassy igneous rocks They are non0crystalline

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Some EXTRUS$E igneous rocks are described as $ESCU*ARmeans that they have many small holes formed as gas escaedthey were cooling

9t@s as if you suddenly solidied the foam that escaed from a casoda that you shook before you oed the to Besicular rocks alike solidied foam

As you can see# some are 1ne 2rained# some are 2lassy# and ale3trusi.e

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Cow let@s look at the #!ERA*S that are found in igneous rock

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Any or all of the mineralsin the shaded area (belocan be found in any of throcks in the shaded area(above)

.ut granite# for examle#would never contain olivior yroxene

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 The same rule alies

to the minerals in the ne'one (shaded) Any or alof these may be found ithe rocks in the shadedarea above

4or examle# 0iorite migcontain .iotite orAmhibole but it is veryunlikely that it would cotain Potassium feldsaror even much $uart'

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2D# by now it should beclear The yellow shadedrocks could contain any oall of the yellow shadedmineralsPeridotite couldonly contain Pyroxeneand,or 2livine and 0unite=667 2livine

So lets put this all to2ether and use the in4ormation to identi4y a sp

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Came a coarse grainigneous rock that containAmhibole# .iotitePlagioclase 4eldsar andPotassium 4eldsar

2D# if it has coarse grainit must be one of theseshaded rocks

Amhibole# Plagioclase and.iotite are no hel because

they are found in morethan one 'one but Potassiu4eldsar is the imortant cl

 The ? clues together oint to onlone ossible igneous rock

GRA!TE5

/et@s try another

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Came a ne grain# vesiculaigneous rock which containPlagioclase feldsar# .iotiteand 2livine

 The only rocks that have ngrain A!, are vesicular areBesicular 1hyolite# BesicularAndesite# and Scoria,Besicul.asalt Cow we have to loo

the mineral content to narrthe ossibilities

 The key is the 2livine whichis found in only one ne gravesicular rock>Scoria6$esicular 7asalt(

2ne last item to understand> haracteristics (those items between theand the minerals)

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 This art is easy 1ocks on the left side are light (in color)# low (density) an$ELSIC. The term 4&/S9 means that these rocks contain a lot of the minefeldsar 9f you look u both kinds of feldsar on age =: of the reference tyou will see that both contain the element aluminum (Al) That@s why (Al) aafter the word 4&/S9 4&/S9 rocks contain a lot of aluminum

1ocks on the right are MA$IC These rocks are usually dark in color# havedensity and contain a lot of iron (4e) and magnesium (!g) The word !A49made u by combining !A from magnesium and 4 from the word ferric whi

describes minerals rich in iron 9f you look u .iotite# Pyroxene# and 2livineage =: of the reference tables you@ll see they all contain iron and magnes

/et@s try one last igneous rock identication

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9dentify a non-vesicular#non-crystalline igneous rocwhich has low density andcontains a lot of aluminum

Con-crystalline could be anof the glassy rocks but only2bsidian and .asaltic lassare both non-crystalline andnon-vesicular .ut which is i

 The low density# 4&/S9rocks (contain Aluminum)are on the left side so therock we@re looking for mustbe 2bsidian

+ait a minuteF Aren@t the lo

density# 4&/S9 rockssuosed to be light colore.ut 2bsidian is usually blac

 True .ut remember that this chart Gust rovides general guidelines Theran almost innite variety of igneous rocks and many don@t t these rules Gust the way it is

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+hat to take a8ay9=) !ake sure you are familiar with the vocabulary +hen you read the word

or B&S98/A1 or P/8T2C9 in a regents $uestion you should know what t  word means and also that you should robably be oening your referenc  to age :

?) 8se information about texture, grain size, intrusive or extrusive, vesicula  non-vesicular to narro8 your choices to certain igneous rocks that t t  information in the $uestion

H) 8se information about the Icharacteristics@ and,or the Imineral comositi  rene your choices to one igneous rock

J) 1emember that the ONL%  way to get good at this is to ractice and rac  some more So nd as many old regents $uestions as you can and see h

  you do 9t@s no diKerent than any sort The more you ractice the bettergetF