EG-07: Rock Cycle
Materials List:
1. Three-dimensional, scaled model of California topography, with geology map of CA and colorcoded interior view of rocks and faults.
2. One box - with compartments, color-coded igneous, metamorphic, and sedimentary rocks for
students.
3. One bag - larger color-coded and name-labeled igneous, metamorphic and sedimentary samples for
EV display.
4. Two containers of sediment - one light-colored sand particles, one darker Franciscan sediment
5. Magnifying glasses
6 Fossil samples
7. Weak HCl acid (for EV use only- it will not harm the skin, just rinse off with cold water). - used
by geologists to identify limestone. Acid on limestone will dissolve the mineral calcite, releasing
carbon dioxide as gas bubbles. If the rock does not fizz, it is not limestone.
8. Glass plates to test for the mineral hardness. If the rock is soft (most carbonates and sulfates) it will
not scratch the glass but rocks with a lot of silica ( granites) will scratch the glass.
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Rock Cycle
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ROCK CYCLE
E.Q. 07
SOURCE:
Bobbie Callison, Murry Hunt
Ray Levine, Mike Mullen
Spring 2000
OBJECTIVES:
1. To illustrate the formation and identification of igneous, sedimentary and metamorphic rock.
2. To demonstrate how plate activity and faulting can result in the formation of Mountains, ocean
deposits, and volcanic activity.
3. To help students understand the processes that cause rocks to change from one type to another
type: igneous, to sedimentary, to metamorphic.
GRADE LEVELS:
4–8
SCIENCE THEMES:
Patterns of change , scale & structure, energy, systems & interactions
SCIENCE PROCESS SKILLS:
Observing, comparing, categorizing, inferring
FOCUS WORDS:
Igneous, sedimentary, metamorphic, plate tectonics, accretion, intrusive, extrusive, subduction,
luster, hardness, Franciscan rock, obsidian, granite, pumice, basalt, shale, conglomerate, chert,
slate, graywacke, schist, gneiss, serpentinite, alluvial, fossil.
BACKGROUND INFORMATION:
Mesozoic Era: (345 - 66 million years ago)
There was no California as we know it today. The western boundary of the North American plate
was somewhere around the Rocky Mountains. The present day Sacramento and San Joaquin valleys
were part of a continental basin ( submerged under water) and filled with marine sediments as well
as volcanic rocks. The Farallon plate existed where the Pacific Ocean is today.
Due to sea-floor spreading at the Pacific mid-ocean ridge, the Farallon plate (oceanic plate) was
pushed slowly eastward toward the North American plate (continental plate). At the same time the
North American plate was pushed slowly westward due to sea-floor spreading at the mid-Atlantic
ridge.
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BACKGROUND INFORMATION (continued):
These events created an active subduction zone as the dense, oceanic Farallon plate was forced under
the lighter, continental North American plate. Friction from the subducting plate, resulted in
temperatures high enough to melt portions of the mantle and crust. The melted area is known as a
magma chamber. Over millions of years the magma cooled. As it cooled, a process of crystallization
occurred, resulting in the formation of granite, one kind of intrusive, igneous rock. Volcanic rock
formed when some of the magma was forced upward through fractures in the earth's crust producing
volcanic eruptions. Basalt, obsidian and pumice are typical extrusive, igneous rocks formed from
such eruptions.
The Sierra Nevada Mountains originated from these magma chambers formed during the Mesozoic
era and contain both extrusive and intrusive igneous rocks. The occurrence of metamorphic rock in
the Sierras is primarily the result of faulting plus extreme heat and pressure that altered rock
surrounding the magma chamber.
As subduction progressed, part of the ocean floor was carried into an existing oceanic trench. Heat
and pressure within the trench metamorphosed much of the rock material. Eventually this ocean rock
was scraped and plastered onto the existing North American continent (a process known as
accretion) to form the Coastal Range Mountains that extend from the Oregon border to just below
Santa Barbara. The result of intense pressure during this process produced a disorderly arrangement
of rocks referred to as the Franciscan complex – metamorphic rocks such as schist, graywacke (a
type of metamorphosed sandstone), greenstone, and serpentinite (California state rock). Serpentinite
is an altered, ocean floor rock formed as hot water circulated through the oceanic crust. Faulting
accompanied this accretion process as evidenced by numerous faults within the Coastal Range
Mountains.
The large, flat Central Valley, which lies between the Sierra Nevada and the Coast Range Mountains,
began as a deep marine basin. It filled with both marine and terrestrial sediments during the
Cenozoic era.
Cenozoic Era: (66 million years ago to the present)
The Sierra Nevada Mountains were uplifted during this period to expose huge granitic blocks
through pre-existing volcanic material. More and more granite has been exposed continuously
through erosion of overlying rock.
Subduction slowed, then ceased after the Farallon plate was totally consumed under the North
American plate. The Pacific plate made contact with the North American plate which resulted in a
directional change. The Pacific plate became a northwesterly moving plate. The boundary between
the Pacific and the North American plate produced a long fractured area, known as the San Andreas
fault. This change in plate boundary motion from subduction to lateral motion caused stresses in the
Sierra region. The blocks of uplifted granite were tilted westward forming the gentle, sloping
foothills of the western Sierras with an opposing steep escarpment on the eastern side. Faulting and
deformation of the earth's crust accompanied these stresses and can be observed in the formation of
Lake Tahoe and Owens Valley.
The Central Valley was a huge basin that alternately filled with fresh water from melting glaciers and
dried up as glaciers re-formed during the various Ice Ages. As the Sierras uplifted and tilted, rivers
carried sediment from the Sierras, filling in the basin. There was no San Francisco Bay at this time,
and Coastal Range Mountains helped to contain sediment in the basin. Over hundreds of years many
layers of sediment have compacted to form mudstone and silt stone that may contain plant fossils.
Most of California as we know it today formed during the last 10,000 years. Approximately 400,000
years ago the Sacramento and San Joaquin rivers cut their way through to the Pacific Ocean at the
present Golden Gate. The once huge basin, now filled with layers of sedimentary rock (e.g. alluvial
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soils - gravel sized), is separated into a Sacramento Valley and a San Joaquin Valley by the
confluence of these two river systems.
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ROCKS:
All rocks fall into one of three types: igneous, sedimentary or metamorphic depending on where
and how they were formed. The California landscape model illustrates intrusive and extrusive
igneous rocks, alluvial and marine sedimentary rocks, metamorphic as well as Franciscan rock.
Rocks are made of minerals and differ from one another by mineral content. Over millions of years
chemical and physical processes change rocks from one type to another. There is no beginning or end
to this rock cycle. Earth is dynamic, constantly changing, as evidenced from the rock cycle.
There are many more kinds of rocks than those included in this kit. The rocks chosen are typical
of this area of CA and were selected for simplicity purposes. Look for the color dot(s) on each
small sample in the rock sample boxes.
IGNEOUS: Color coded RED if intrusive and PINK if extrusive (volcanic)
Rocks that are formed by heat deep in the earth's interior are in this classification. Igneous rock is
created when magma melts due to plate movement, then cools and minerals crystallize into rocks
The igneous rock formed during plate collisions may be uplifted as a huge mountain chain or
exposed on the ocean floor during sea-floor spreading and during volcanic eruptions.
If crystallization occurs slowly beneath the earth's surface (intrusive), then the minerals form coarse grained rock such as granite. If crystallization occurs above the earth's surface (extrusive), the
minerals cool faster to form fine-grained rocks such as basalt or cool very fast to form a shiny, glasslike obsidian rock. If gases are present in the melted rock, pressure may cause a volcanic eruption
and the resulting rock would be porous as the gases escape during crystallization (pumice).
Igneous rocks undergo weathering (freeze and thaw) to crack and disintegrate. This fragmented
material called sediment is picked up by running water, wind, or glaciers and transported to a new
area. Sedimentary rock can be formed from these sediments by compaction and "gluing " together of
the sediments.
Igneous Rock Samples:
Granite - composed primarily of the minerals quartz, feldspar and mica, intrusive rock that was
cooled slowly, then uplifted to create the Sierra Nevada range - pink, white, black color
Basalt - lava rock- little silica, mostly iron and magnesium, extrusive so it is fine-grained, found
on sea-floor, some from volcanic eruptions, found along coastal ranges, or in the Sierras
Obsidian -shiny black, extrusive also called volcanic glass due to high percentage of silica, on
the east side of the Sierras produced by volcanic eruptions.
Pumice - volcanic rock, extrusive with gases mixed in magma, very lightweight, found in the
Sierras
SEDIMENTARY: Color coded YELLOW OR GOLD
These "settling" rocks formed by weathering and erosion processes are transported by rivers to new
locations such as a lake, valley, San Francisco Bay, continental shelf and ocean floor. Each year as new
sediment arrives, it is deposited to form layers of sand, silt or mud. The sediments are compacted by the
weight of the new material on top of them and may be cemented together by silica, calcium carbonate or
iron oxide to form sedimentary rock (conglomerate, sandstone, silt stone, mud stone). Fossil sea shells
can provide the mineral calcium carbonate or lime as a cementing material (evident in limestone rock).
Fossils are found only in sedimentary rocks (limestone, shale). Most of the material children see on the
earth's surface (gravel, sand, clay, pebbles, conglomerates) are sediments or sedimentary rock.
Sedimentary Rock Samples
Non-marine - terrestrial or alluvial; color-coded YELLOW
Sandstone - uniform particle size, found along the coastal range, alluvium, pink to gray
Conglomerate - different particle sizes, cemented and compacted together.
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Mud stone or silt stone - lakes, ponds, marshes, cemented silt and clay particles, may contain
plant fossils.
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Marine – color-coded GOLD
Chert – high percentage of silica, strong rock, red or green color, found along the coastal range
especially the Marin headlands
Limestone - (calcium carbonate) found along the coastal range and central valley, gray or white
Sandstone - sand-sized particles, may contain marine invertebrate fossils, found along the coast
range, gray to tan
Shale - small silt and clay particles with parting along its layers, very dark gray, may contain
trilobite fossils from the Paleozoic era.
METAMORPHIC: Color - coded BLUE or GREEN if Franciscan complex
Rocks formed deep in the earth's interior. Tremendous pressure and heat from over-lying rocks will
cause under-lying rock to change its appearance as the minerals in the rock re-arrange to form new
patterns. Igneous and sedimentary rocks can be altered in this manner. Often, the result is a banded
appearance (gneiss - originally shale or granite) or changed appearance when minerals become
recrystallized (slate - originally shale or marble - originally limestone). If metamorphic rock is
subject to even greater heat, it may melt creating magma that will eventually crystallize to form
igneous rock (gneiss can melt to form granite).
The Franciscan complex is a mish–mash of several metamorphosed rock types unique to the Coastal
Range Mountains. Serpentinite, California's state rock, is in this category. By-products of this rock
are soapstone (an impure talc rock, note slippery feeling), talc, and asbestos (chrysolite).
Metamorphic Rock Samples: Color-coded BLUE
Marble -parent rock is limestone, found in the Sierras and Santa Cruz mountains.
Slate - black or red, the parent rock is shale or mud stone, a weak rock that splits into sheets,
located in Sierra foothills.
Gneiss – has alternating bands of micas and quartz, feldspar, found in the Sierras.
Schist- has a scaly, flaky look, blue schist is found in the Sierra foothills.
Franciscan Complex: Color coded GREEN
Graywacke - metamorphosed sandstone, found on edge of North American Plate.
Serpentinite - altered ocean floor rock, greenish black, found along the coastal ranges, foothills of
the Sierras and Jasper Ridge and Los Trancos areas.
ACTIVITIES:
• Lift the land-form model out of box, using the tab holder. Return by hanging on to the holder,
place the other end in box first and leave tab out, ready for the next person to use..
• Note black square area on geology map of CA in top of box. This is the section of the 3-D
topography model. If you wish to discuss rivers on the model, they are labeled on the map. Cities
of San Francisco, San Jose and Sacramento are identified with white pinheads for area
perspective. Mt. Tamalpais and Mt. Diablo can be identified as well as Lake Tahoe and San
Francisco Bay.
• Present children with some highlights from the background information. Tell children that rocks
can tell a story about where they came from. Use the large rock samples for visual identity so
they have sufficient knowledge about general rock types and their formation. (5 minutes).
•DIFFERENT WAYS TO USE THIS KIT –
1. Guessing game about rock formations (10 minutes)
Materials: Wooden box of small rock samples for children and the bag of large samples for
display. Place the large samples on the appropriate family rock name: Igneous, Sedimentary,
Metamorphic. Do not let the children see the labels inside the wooden box compartments.
Divide the group into pairs.
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Give each pair a small rock sample to observe for a minute. Discuss interesting features of that
rock Can they identify the family their rock belongs to?
Why do the rocks have different colors, shiny, dull, hard, soft, light, heavy, fossils?
Ask each pair of students to indicate on the model where their rock was formed or would be
found (river, central valley, Sierras, beach, deep in the interior).
Repeat the process with another rock for each student pair for as long as time allows.
DO NOT place rocks on the model as they may damage the finish.
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OR
Place the large labeled samples in the center of the table.
Repeat the above steps except ask students to identify their rock type and name of rock. They can
compare with their small samples.
2. Properties of minerals (10 minutes)
Divide the group into pairs. Pass out marble, granite, shale, serpentinite, sandstone, limestone,
obsidian, basalt, pumice. Each pair can do one or more tests and compare results with other pairs.
Geologists test rocks for their mineral content in several ways. Some of these tests will indicate
where the rock was formed.
a) Luster – (how light shines off the rock - obsidian is very shiny while basalt is dull.
Ask: Did the rock cool slowly or rapidly? (indicates where formed - intrusive or extrusive)
b) Hardness testing – (how easily can the rock be scratched or scratch glass )
Ten different minerals are used to represent degrees of hardness, ranging from 1 (very soft) to 10
(extremely hard), they are:
#1 Talc
#4 Fluorite
#7 Quartz
#10 Diamond
#2 Gypsum
#5 Apatite
#8 Topaz
#3 Calcite
#6 Feldspar
#9 Corundum
A mineral of unknown hardness can be compared to an object of known hardness. Common
objects used to test hardness are: a fingernail – has a hardness of 1 to 2.5, copper coin is 3 ,
while a glass plate is 5.5. Test each of the small rock samples with one of the objects and ask
students to rate its hardness. They can confer and then arrange their samples with the softest at
one end, hardest on the other end.
Ask: How fast do you think your sample change into another rock type?
How well will it hold up during an earthquake, heavy rains?
Which rock type would you want in your home for floors, bathroom basin?
Which rock is more likely to be involved in landslides - granite or shale?
What type of soil do you want your home to be built on? ( Mention the 1996 Yosemite
landslide in which granite over millions of years weathered and weakened).
c) Specific gravity – (How heavy is the rock: e.g. how many of the rock’s atoms/molecules are
packed into a specific space?) e.g. pumice is light due to air pockets compared to basalt that
contains many bonded atoms. The darker the rock, the more iron it contains and the heavier
(high specific gravity) it is - e.g. compare granite to basalt.
Ask: Where did each rock form on the model.
d) EV Does This – Use the large limestone rock and place one drop of dilute hydrochloric acid
(HCl) on its surface. Marine sedimentary rock can be tested with weak acid for the presence of
calcium carbonate which acts as a glue to hold particles (sediments) together. Place a drop of
HCl on a sample.
Ask: Why did the rock fizz? This is proof that the rock contains calcium carbonate and has
released carbon dioxide as a result of a chemical reaction with HCl.
What was released?
Show the seashell and talk about the source of calcium in sedimentary rock (comes from shell
bits).
Ask: What will happen if a drop of HCl is put on the shell? What does this tell us?
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3. OPTIONAL (for older students, 5 – 8)– You may want to concentrate on the Sierras and the river
system that carries sediment to the Central Valley, San Francisco Bay and the ocean beaches.
The rock model shows the Sacramento river in the north and San Joaquin river in the south, both
converge in the San Francisco Delta. West flowing rivers from the Sierra foothills are: (from
north to south) Feather, Yuba, American, Mokelumne, Stanislaus and Tuolomne.
Mechanical and chemical weathering (alternating heat with cold, ice, wind, acidic rain) causes
granite chips of various sizes to break off that can be carried by streams and rivers across the
landscape. Some of this sediment is deposited along the way in river bottoms, ponds, lakes or
bays. San Francisco Bay contains mud and silt carried by these rivers.
Some sediment may reach the continental margin to become beach sand.
Show students the bottled samples of sediments. The lighter one is typical of a Santa Cruz beach
with many light-colored quartz sand particles. This sediment may have traveled from the Sierra
Nevada.
The darker sample is from a beach in Marin that has more sediment from the Coast Range
Mountains with Franciscan rock, originally from the ocean floor.
Use magnifying glasses to identify different sediments in the samples. Are the sediments round
or maybe shiny (acted on by chemicals in water or wave eroded)? Are they angular (little water
erosion)? Are they opaque or frosted in appearance (carried by wind)?
Ask: Why do we need to dredge the San Francisco Bay periodically?
Why are the sands at Santa Cruz different color from the sands at a beach in Marin?
Would the sands be different in Hawaii or Florida?
Ask students if they have been to a beach in a different part of the world or the United
States?
Does the appearance of a sediment tell you where it came from and how it got there?
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