1. Rocks
Ch. 6

2. How Rocks Form ch. 6 sec. 1 What is a Rock?
a solid made of 1 or more minerals
also can contain organic matter ex. Coal
In which of Earth’s layers (crust, mantle, core) are rocks found?
crust & mantle
What is a rock? an aggregate of minerals, a group of minerals bound together, a solid composed of more than one mineral
Can consist of mostly one mineral or several different minerals in varying quantities… also can contain organic matter ex. coal
In which of Earth’s layers (crust, mantle, core) are rocks found? Crust & mantle… we generally see the rocks of the crust
BrainPop 3 Types of Rocks

3. What is a Rock? What are the 3 types of rock found in Earth’s crust?
igneous
sedimentary
metamorphic
How do we classify these 3 types of rocks?
according to how they formed
cooling & hardening of hot, molten rock (magma)
compaction & cementing of layers of sediments (rock fragments, plant & animal remains, minerals that settle out of solution onto lake/ocean bottoms, or water that evaporates & leaves behinds minerals)
effect of heat & pressure on other rocks
BrainPop 3 Types of Rocks

4. The Rock Cycle What is the rock cycle? What causes the rock cycle?
gradual & continuous process that causes rocks to change from one form to another
What causes the rock cycle?
interactions between water, air, land
What causes the rock cycle? interactions between water, air, land  weathering, erosion, deposition, compressive forces, stretching forces, rubbing forces, heating, pressure
Rock Cycle Movie

5. The Rock Cycle ESRT pg. 6

6. What Can Happen to Igneous Rocks?
1. Heat & pressure/ “metamorphism” metamorphic rock
2. Melt to form magma which solidifies  igneous rock
3. Weathering & erosion form sediments which are deposited, buried, compacted, & cemented sedimentary rock 3 1 2

7. What Can Happen to Sedimentary Rocks?
1. Heat & pressure/ “metamorphism” metamorphic rock
2. Melt to form magma which solidifies  igneous rock
3. Weathering & erosion form sediments which are deposited, buried, compacted, & cemented sedimentary rock 3 2 1

8. What Can Happen to Metamorphic Rocks?
1. Heat & pressure/ “metamorphism” new metamorphic rock
2. Melt to form magma which solidifies  igneous rock
3. Weathering & erosion form sediments which are deposited, buried, compacted, & cemented sedimentary rock 1 3 2

9. Igneous Rocks ch. 6 sec. 2 Igneous Rock Formation
How are igneous rocks classified?
By mineral composition & texture
What do igneous rocks form from?
molten rock (magma/lava) or volcanic ash
What happens as the material cools?
crystals grow & interlock
rate affects size of crystals
What happens as the material cools? crystals grow & interlock, rate affects size of crystals…. Slow = large crystals, fast = small (or no) crystals
Igneous Rock Formation Movie

10. Igneous Rock Formation
How can we classify the magma/lava that forms igneous rocks?
felsic
large amounts of silica (& aluminum)
small amounts of calcium, iron, magnesium
thick, sticky, slow-moving (high viscosity)
low density
typically forms light-colored minerals
mafic
large amounts of iron & magnesium
Small amounts of silica
thinner, runnier (less viscous)
high density
typically forms dark-colored minerals
Magma may be classified as felsic, mafic, or an intermediate form.
Felsic magma: thick and slow moving (high viscosity… resistance to flow); large amounts of silica (SiO2) and small amounts of calcium, iron, and magnesium; typically hardens into rocks containing light-colored silicate minerals (ex. quartz and postassium/orthoclase feldspar)
Mafic magma: hotter, thinner, more fluid; large amounts of iron and magnesium and smaller amounts of silica; typically hardens into rocks containing dark-colored silicate minerals (ex. amphibole/hornblende, augite, biotite)

11. Magma may be classified as felsic, mafic, or an intermediate form.
Felsic magma: thick and slow moving (high viscosity… resistance to flow); large amounts of silica (SiO2) and small amounts of calcium, iron, and magnesium; typically hardens into rocks containing light-colored silicate minerals (ex. quartz and orthoclase feldspar)
Mafic magma: hotter, thinner, more fluid; large amounts of iron and magnesium and smaller amounts of silica; typically hardens into rocks containing dark-colored silicate minerals (ex. hornblende, augite, biotite)

12. Igneous Rock Formation
What are the 2 types of igneous rocks?
intrusive & extrusive
How do intrusive igneous rocks form?
form from magma inside Earth
cools slowly
How does that affect the crystal texture (size)?
medium to coarse (easily seen)
How do extrusive igneous rocks form?
form from lava (or ash) that has exited Earth
cools quickly
glassy (no crystals) to fine (not easily seen)
can be vesicular
What are the 2 types of igneous rocks? Intrusive (aka plutonic igneous rocks) & extrusive (aka volcanic igneous rocks)
How do intrusive igneous rocks form? Form from magma inside Earth, Cools slowly
How does that affect the crystal texture (size)? Medium to coarse (easily seen) b/c cools slowly which allow crystals more time to form
How do extrusive igneous rocks form? Form from lava (or ash) that has exited Earth, Cools quickly
How does that affect the crystal texture (size)? Glassy (no crystals) to fine (not easily seen) b/c cools quickly which does not allow crystals to form or if they do form, they do not have time to get big… Can be vesicular (holes due to air bubbles that were trapped or burst during formation)
Igneous Rock Formation Movie

13. Igneous Rock Descriptions
How do we group igneous rocks into different “families”?
according to mineral composition
How can we recognize/ID specific igneous rocks?
color
determined by mineral composition
texture
size & arrangement of crystals

14. Igneous Rock Descriptions
Granite Family/Felsic Rocks
What is the composition of felsic magmas?
silica (& aluminum)
thick, sticky, slow-moving (high viscosity)
What minerals are typically found in felsic rocks?
quartz, feldspar, mica, amphibole/hornblende
What are other common characteristics of felsic rocks?
light color
low density
Examples:
pegmatite, granite, obsidian, pumice, rhyolite
Granite Family/Felsic Rocks Form from felsic (silica SiO2 and aluminum-rich) magmas
Usually coarse-grained because their slow-rising, “sticky” parent magmas tend to cool slowly underground
Typically contain quartz, feldspar, mica, amphibole/horneblende, Light-colored, Low in density
Granite: one of the coarsest-grained rocks in this family Intrusive
Often contain large amounts of light-colored feldspar color of feldspar determines rock color white or gray to pink
Very common continental rock found in many mountainous areas across the U. S.
Obsidian: Glassy texture (no crystals) Extrusive
Chemically similar to granitic rocks even though it is usually dark brown or black (when thick, thin slices appear lighter)
Pumice: Forms when silica-rich lava Extrusive
hardens as steam & other gases bubble out of it causing Vesicular texture Resembles a sponge because of holes and air pockets
Often able to float on water
Felsite: General name for any light-colored, fine-grained rock
Rhyolite is a common example Fine-grained, ranges from light gray to pink

15. Igneous Rock Descriptions
Gabbro Family/Mafic Rocks
What is the composition of mafic magmas?
iron and magnesium-rich (silica poor)
thinner, runnier (less viscous)
What minerals are typically found in mafic rocks?
pyroxene, olivine, plagioclase feldspar (amphibole & biotite mica)
What are other common characteristics of mafic rocks?
dark color
high density
Examples:
gabbro, basalt, diabase, basaltic glass, scoria
Gabbro Family/Mafic Rocks Form from mafic (iron and magnesium-rich/silica poor) magmas
Typically contain pyroxene, olivine, plagioclase feldspar (amphibole and biotite mica) Dark in color High density
Gabbro: coarse-grained rock very dark color
Basalt: Composition similar to gabbro fine-grained, dark gray or black Most common rock in gabbro family
On land (including underwater), most common rock Makes up the ocean floor formed from lava flows
Diabase: texture is finer than gabbro but coarser than basalt
Basalt glass: resembles obsidian but is mafic
Scoria: (like pumice) full of holes, darker and denser than pumice, holes are usually larger, unlikely to float

16. Igneous Rock Descriptions
Diorite Family/Intermediate Rocks
What is the composition of intermediate magmas?
neither felsic or mafic… has characteristics of both
What are other common characteristics of mafic rocks?
intermediate color
medium grays & greens
darker than felsic, lighter than mafic
medium density
Examples:
diorite & andesite
Diorite Family/Intermediate Rocks
Diorite: coarse-grained, has less quartz than granite and less plagioclase feldspar than gabbro
Andesite: fine-grained
Other Igneous Rocks
Felsic-intermediate: granodiorite
Ultramafic: peridotite, dunite, pyroxenite Hypothesized to be similar to rocks in Earth’s mantle

17. Identifying Igneous Rocks
Start w/ texture/grain size (& if vesicular or not) to narrow down & help determine if intrusive or extrusive
Then look at color (light, in between, dark) & mineral composition (and approximate percentages if needed using ruler along left to help gauge percent/range of percents of each mineral type)
Ex. Coarse, non-vesicular texture light-medium color contains pink, white/colorless, black minerals  feldspar, quartz, biotite, amphibole

18. Igneous Intrusions Dike: vertical, in between rock layers
Laccolith
Volcanic neck
Sill
Volcano
Batholith
Stock
Dike
Pluton: any rock mass that forms when magma pushes into fractures (cracks) in the bedrock
Examples:
Dike: vertical, in between rock layers
Sill: parallel to rock layers it intrudes Ex. Palisades Sill along the Hudson River (NY/NJ)
Laccolith: domed mass, bulge
Volcanic neck: central plug of hardened magma left after the volcanic material around it has worn away
Batholith: largest of all plutons, cores of many mountains
Stock: a small batholith that is exposed at the surface

19. Sedimentary Rocks ch. 6 sec. 3 Formation of Sedimentary Rocks
Where are most sedimentary rocks found?
covering the surface of Earth’s crust
In general, how do sedimentary rocks form?
compaction & cementing of layers of sediment
How are sedimentary rocks classified?
by 3 basic formation processes
What are the 3 major types of sedimentary rocks?
clastic
chemical
organic

20. Clastic Sedimentary Rocks
How are clastic sedimentary rocks formed?
weather forms fragments of rock (sediments)
Usually eroded (transported) by running water
sediments are deposited
layer after layer as the water slows down
sorted by largest sediments first, smallest last
Why?
compacted
as layers pile up
cemented together by minerals (dissolved in water)
cement influences color (silica, calcite, iron oxide, clay)
Sorted by largest sediments first, smallest last Why? As energy decreases (usually due to decrease in speed) largest/heaviest particles are first to be dropped b/c can still carry smaller/lighter particles… as slow down more & more, medium then small particles drop out

21. Deposition & Sorting of Sediments
If given velocity… see where intersects w/ line on graph…. And look to left/right to find largest particle size that the water can carry (and all sizes below)
If given particle size… see where intersects w/ line on graph…. & look down to see lowest velocity at which that particle size can be carried
If given velocity, see where intersects w/ line on graph….
look to left/right to find largest particle size that the water can carry (& all sizes below)
If given particle size, see where intersects w/ line on graph….
look down to see lowest velocity at which that particle size can be carried

22. Clastic Sedimentary Rocks are Classified by Particle Size
Smallest to largest
silt & clay particles shale/siltstone
sand particles sandstone
mixed particles conglomerate/ breccia

23. Chemical Sedimentary Rocks
How are chemical sedimentary rocks formed?
when minerals precipitate (fall out) of water
What cause mineral precipitation?
evaporation
sea or lake dries up leaving behind minerals that were dissolved in water
chemical action
dissolved ions combine to form new minerals
left: salt flats right: the white cliffs of Dover (England) made of limestone
Also referred to as crystalline sedimentary rocks

24. Chemical Sedimentary Rocks
Examples:
Rock Salt
Rock Gypsum
Limestone (travertine)

25. Organic Sedimentary Rocks
How are chemical sedimentary rocks formed?
from sediments consisting of the remains of plants and animals
Examples of organic sedimentary rocks
limestone (& coquina)
coal
Limestone contain mineral calcite
Begins when water dissolves calcite out of rocks on land & carries it in the form of calcium ions to ocean or lake
Certain organisms use the ions to produce calcium carbonate shells or other support structures
When die, remains pile up on ocean floor
Masses of complete & nearly complete shells can be cemented together (coquina)
Small shell fragments cemented together  limestone

26. Organic Sedimentary Rocks
Shells
 Fossil
limestone
Contain the mineral calcite

27. Organic Sedimentary Rocks
Plant remains  coal
peat
lignite
bituminous
anthracite

28. Features of Sedimentary Rocks
stratification
fossils
ripple marks
mud cracks
nodules
concretions
geodes
Stratification arrangement of visible layers result from changes in sediment type being deposited
Bedding planes (lines between the layers) show where the layers are separated Usually horizontal, but cross-bedding (angled deposits) can occur Occur for a number of reasons New types of rocks picked up (from different locations)
More of different types of rocks carried during flooding Sediments carried longer or shorter distances
Fossils the remains, impression, or other evidence of a plant or animal preserved in rock occur when dead organism is buried by sediments and gradually turns to rock Usually only hard parts are preserved
Impressions occur when shell, skeleton, etc. is pressed into soft sediments
Ripple marks = sand patterns formed by the wind, streams, waves, or currents
Mud cracks = develop when wet clay dries and contracts (shrinks) Cracks fill with different sediments & fossilize
Nodules = lumps of fine-grained silica in limestone or chalk Ex. chert and flint
Concretions = round, solid masses of calcium carbonate form when minerals in dissolved in water precipitate around shell fragments or other impurities in clay sediments Ex. Oolites
Geodes = spheres of silica rock found in limestone Inside lined or filled with crystals (quartz or calcite)

29. Identifying Sedimentary Rocks
1st, determine texture (clastic, crystalline, bioclastic)
2nd, if clastic…. grain-size & comments
if crystalline, try to determine mineral composition (halite  looks & tastes like salt, dolomite  when powdered, bubbles in acid, gypsum generally looks powdery & white/beige/pink)
if bioclastic… comments…. (shells? Fossils? Plant remains?)
try to determine mineral composition (calcite  bubbles in acid, carbon  generally dark in color)

30. Metamorphic Rocks ch. 6 sec. 4 Formation of Metamorphic Rocks
In general, how do metamorphic rocks form?
formed from “parent rock” that has undergone metamorphism
pressure & heat
Earth’s internal heat
weight of overlying rock
deformation of rock as mountains build
moisture
hot liquids (& gases) from magma that react with minerals

31. Formation of Metamorphic Rocks
How do metamorphic rocks compare to parent rocks?
may resemble parent rock
may have a chemical composition, texture, or internal structure that differs from parent rock
minerals may be enlarged or reformed
new minerals may appear
rock may become more dense & less porous (less “empty” space)
Often resembles “parent rock” Differences are the result of metamorphic processes that the “parent rock” has undergone
A metamorphic rock may have a chemical composition, texture, or internal structure that differs from the parent rock.
Minerals may be enlarged or reformed
New minerals may appear
The rock may be more dense and less porous (less “empty” space)

32. Metamorphic Processes
What are the 2 basic types of metamorphism?
regional
local
Metamorphism the process by which a rock’s structure is changed by pressure, heat, moisture

33. Metamorphic Processes
What is regional metamorphism?
Large-scale
intense heat & pressure (ex. mountain building)
pressure greater in one direction  minerals align in layers (perpendicular to force)
can cause folding of rock layers
Limestone
Marble
gneiss
schist
phyllite
slate
shale
Lime
quartzite
sandstone
Metamorphism the process by which a rock’s structure is changed by pressure, heat, moisture
Regional Forms most of the metamorphic rock of Earth's crust Often occurs over very large areas Can occur during mountain building
Due to intense heat and pressure Temperature increases with depth Pressure increases w/ depth (more overlying rock) Pressure greater in 1 direction, minerals align in layers Different amounts of heat & pressure  different amounts of metamorphism. Higher temperature & pressure  greater metamorphism Can cause folding of rock layers
forms most of the metamorphic rock of Earth's crust

34. Metamorphic Processes
What is local metamorphism?
occurs over smaller, more distinct areas than regional
two types
contact
hot magma “bakes” rock
deformational (dynamic)
low temperature, but high pressure
areas of stress & friction
ex. plate boundaries
changes to texture & structure of minerals (not composition)
Local Smaller, more distinct areas
Two types
Contact:
Occurs when hot magma moves into rock, heating and changing it.
Causes fewer changes and affects much less rock than regional metamorphism
Deformational (aka dynamic):
Occurs at relatively low temperatures and high pressure
Caused by stress and friction (often at faults where rocks move against each other)… mountain building, transform plate boundaries
Mineral composition usually stays the same, but texture and structure may change

35. Metamorphic Rock Descriptions
description & ID usually based on texture, grain size, mineral content, & parent rock
2 main types
foliated
mineral alignment (due to pressure)
often different colored bands (“banding”)
may look scaly
often split along parallel layers
non-foliated
don’t show mineral alignment or banding
look crystalline (sparkly or sugary)
Description and identification usually based on parent rock, mineral content, and texture
Foliated Metamorphic Rocks
Minerals flattened by pressure producing mineral alignment at 90 degree angle to direction of pressure, may also cause minerals to differentiate into different colored bands
Nonfoliated Metamorphic Rocks
don’t show mineral alignment or banding
look crystalline (sparkly or sugary)

36. Foliated Metamorphic Rocks: Examples
granite  gneiss
shale  slate  phyllite  schist
(Extreme Metamorphism)

37. Non-foliated Metamorphic Rocks: Examples
Limestone  marble
Sandstone  quartzite
Conglomerate  metaconglomerate

38. Identifying Metamorphic Rocks
1st determine texture
2nd determine grain size
3rd, if possible, determine mineral composition
4th, use comments to help make final ID if necessary