Rocks
3 types of rocks
• igneous
• sedimentary
• metamorphic
1. Igneous rocks (fire-formed)= rock that solidified from a molten state
• majority of crustal rock (although it is often covered with sedimentary rocks)
• consists of silicate minerals w/ metallic elements
• “interlocking grains”
e.g. granite, basalt, obsidian, pumice
Magma: molten rock beneath Earth’s surface
GraniteBasalt
ObsidianPumice
Composition of igneous rocks
Felsic Mafic
Elements Si & Al Fe & Mg
Melting pt low temp. high temp.
Density low (light) high (heavy)
Color light dark
e.g. granite, diorite basalt, gabbro
Global Composition Distribution
Continents- Felsic
Oceans- Mafic
Digital Elevation Model (DEM)
Cooling and crystals
Slow cooling = bigger crystals
Fast cooling = smaller crystals
So, the cooling history of an igneous rock determines how big its crystals will be
Intrusive“Plutonic”
• cools slowly under the surface
• large crystals
• e.g. granite
Extrusive“Volcanic”
• cools quickly above the surface
• small crystals
• e.g. basalt
Felsic Intermediate Mafic
Intr
usiv
eE
xtru
sive
Rhyolite
Classifying igneous rocks
Andesite Basalt
Granite Diorite Gabbro
RhyoliteRhyolite
AndesiteAndesite
BasaltBasalt
GraniteGranite
DioriteDiorite
GabbroGabbro
YellowstoneYellowstone
Sierra NevadaSierra Nevada
AndesAndes
Ocean basementOcean basement
HawaiiHawaii
New ZealandNew Zealand
Intrusive features
batholith dike(vertical)
sill(horizontal)
Pluton: body of intrusive rock
Famous extrusive rocks
Famous intrusive rocks
2. Sedimentary rocks= formed through erosion, transportation,
deposition, compaction, cementation, and hardening of sediment
Sediment = fine-grained mineral matter transported by air, water or ice
• accumulates at low elevations to form strata (rock layers)
Sedimentary rocks
• majority of surface rock• often fossiliferous• e.g. sandstone, shale, limestone, coal
Classifying sedimentary rocks1. Clastic2. Chemical3. Organic
Classifying sedimentary rocks1. Clastic
- derived from weathered & fragmented rock
- boulder microscopic grain sizes- e.g. mudstone, shale, sandstone
Sandstone Shale
Classifying sedimentary rocks2. Chemical
- dissolved minerals - transported in solution & precipitated- e.g. limestone, evaporites
Limestone
Halite
Classifying sedimentary rocks3. Organic
- remains of dead organisms- e.g. coal
CoquinaCoal
Famous sedimentary rocks
3. Metamorphic rocks (change form)
• rocks changed by heat &/or pressure
• changes structure, appearance , composition, & texture of parent rock WITHOUT MELTING IT
• commonly at roots of mountains
e.g. slate, schist, gneiss
Metamorphic processes
3. Metamorphic rocks
limestone marble
sandstone quartzite
granite gneiss
shale slate schist
Somewhat famous metamorphic rocks
Rock Identification• Break into groups of 4, 5, or 6• Have one person come up and get a set of 3
rocks.• Use the flow chart on the following slide to
identify your rocks.• Determine the type of each rock (igneous,
sedimentary, or metamorphic).• Write your names, rock ID #’s, rock names, and
rock types on a sheet of paper to hand in.
Granite BasaltSandstone ShaleLimestoneGneissSchist
Can you see the mineral grains?
Are the grains interlocking, or cemented together?
Are there layers or stripes(foliation) to the grains? yes no
interlocking cemented
yes no
Is the rock “scaly” or “glittery”?
yes no
Is it very dark colored (mafic)?
yesno
Definitive test: Does it react to a weak acid by “fizzing”?
Ok substitute test for today: is it layered in flat sheets?
noyes
yes no
Double check: is it layered in flat sheets?
noyes
IncludeRock #Rock NameRock Type
Answer key
Granite
Basalt
SandstoneShale
Limestone
Gneiss
Schist 2
1
3
5
4
6
7
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