All about rocks

3.  Igneousrocksareformed whenliquidmagma coolsand hardenseitherinside
theearthunderthecrust,oroutsidetheearth after a volcanohaserupted.When
themagma coolsslowlydeepbelowtheearth'scrust,crystalsformandtherock
becomescourseandgrainywithpocketsof "air bubbles".When themagma
coolsrapidlycloserto theearth'ssurface or outsidethesurfaceafter aneruption,
thecrystalsthat form are smallerand afinegrainrockisformed. Igneousrocks
can take ona variety ofdisguisesbecauseof allthedifferentpossiblechemical
make-upsofmagma andthedifferentcoolingratesthatthemagma hardensat.
Geologistshave togiveigneousrocks a deeperlooktoreallydetermine what
typeofrockitis.

5.  Sedimentaryrocks are the"regularJoes" ofrocks. Over75% ofthe rocks on this
Earth aresedimentaryrocks. These typesof rocks areformedas sediments; such
as sand, pebbles, minerals,plants or animals,andaremovedtogether bya force
likewater. Overtime, thesediments form layersand hardenintorock. This
formationprocesscan leadtothe creationoffossils. Fossils formwhena plant,
animal,or track iscaptured in the layersofthe rock and arepreserved
forever.Some ofthe sedimentaryrocksare held together byan electrical
attraction,while others remainloose andbrittle.This type of rock can be
characterizedbydistinct layersofrock that run paralleltoeach other andcan
evenlook likestripes. Generally,the rocks are fairlysoft and can break apartor
crumble easily.

7.  Metamorphicrocksare formedwhenigneousrocksor sedimentaryrocksare
underan extreme amountof heat and pressure.Therocks don'tactuallymelt.
Theyundergoa metamorphosis(hencethename,Metamorphic).Therocks
are undersomuchpressureandextremeheat that theyphysicallychangeor
reactwith otherrocks or fluidsbelowthecrust.Thesetypesof reactionscan
createthelookof bandsorstripesto disguisetherocks.Theybecomedenser
andmore compactrocksandcanhave shinycrystalsthat formed duringthe
chemicalreactions.Metamorphicrocksholdan additionalelementof mystery
for geologistssincetheyare formed from change,andgiventheright amountof
heat andpressure,theycanchange again.

11.  Types of Rocks Video
 Rock Cycle Video