Name(s): ____________________________________________________
For Busch & Tasa 9th ed. 2011
Section (please circle one): 1 2
Lab 4: Rock-Forming Processes and the Rock Cycle - I
This lab is worth 140 points and 2% of the total marks for the course. The aim of
this lab is to introduce you to rocks and some physical characteristics of rocks which help
you infer how the rocks formed. Rocks are comprised of minerals or of pre-existing rock
fragments made of minerals. Silicates are most common, but carbonates, oxides, sulfides
and mineral-like substances such as agate, opal and coal also occur. Rocks are really
mineral assemblages which reflect the kinds of minerals which occur together because of
the processes which assembled them, or are thermodynamically stable together because
of the rocks chemical composition and physical conditions of formation. Finding and
identifying some of the minerals present provides clues as to which other minerals might
also occur. Identifying the minerals that make up a rock relies on the physical and
chemical tests you have already worked with in addition to the optical characteristics and
fine scale textures visible under a petrographic microscope in thin section.
To do this successfully, you must be able to identify their constituent minerals so
use some of the lab time to ensure that you KNOW the major rock-forming minerals.
In addition to the tables in Lab 4 to help you recognize and distinguish the 3 main rock
groupings: Igneous, Sedimentary and Metamorphic, you will need to refer back to the
mineral identification tables in Ch 3 and to look ahead to the more detailed tables for
each group in the subsequent 3 chapters: 5, 6, and 7.
Turn to Lab 4, and read p. 89-99 in the lab manual. Read the information and
view the diagrams. Inspect the rock kits for each of the 3 rock groups and the larger
labeled specimens. Learn the principal differences among the groups such as where they
occur, how they form, what minerals comprise them and what special textures they
exhibit. An example of each of the 3 rock types follows. 1) Shales are a fine grained
sedimentary rock with pronounced fine scale layering on the scale of a few mm. They are
made of clay minerals and other very fine grain sized mineral particles of quartz, calcite,
iron oxides. They are found in basins along with other sediments. They form by the
weathering and transport of other pre-existing rocks. 2) Ignimbrites or welded tuffs are
fine grained partly glassy and partly fine-crystalline explosive volcanic rocks. They are
typically flow folded and often contain flattened glass shards shaped like the letter Y and
flattened gas pockets called vesicles. They were deposited subaerially by explosive ringof –fire, gas-rich rhyolitic volcanoes in subduction zone settuings. 3) Skarns are unusual
coarsely crystalline but usually equant textured metamorphic rocks formed in
hydrothermal and ore deposit settings. They typically contain quartz, epidote, garnet,
diopside and often metal-sulfide ore minerals like chalcopyrite or pyrrhotite. These form
on the geolocial contact between intermediate plutonic rocks and dirty or clay and sand
bearing limestones. While these examples give you a lot of new terms to consider, each
rock has special minerals, textures and settings in which they occur or processes by
which they are formed. Other rock and mineral guides are helpful to get you started
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Answer the question from the manual in the corresponding spaces provided
on the accompanying charts.
Activity 4.1: Introduction to Rocks and the Rock Cycle
A-1) Inspect the Figure on p. 99. Complete this circular rock cycle figure by colouring
the arrows for the processes which make or characterize each of the 3 rock types. Colour
any arrow which results in a sediment or creates a sedimentary rock yellow. Colour any
arrow which results in a metamorphic rock green. Colour any arrow which results in an
igneous rock red. Note: it is the process which counts here and the final product, and not
necessarily what it was to begin with! (11 pts)
A-2) Complete the table below the figure and place an x in the column of some of that
type of rock contains this feature or is formed by this process. This requires some reading
and is a bit tricky as you can lose points for not putting in an x where you should or for
putting in an x where you shouldn’t! (15 pts)
Activity 4.1: Rock Photos and the Rock Cycle
Weathering and Sediments: All sediments form from pre-existing detritus or
dissolved ions in waters at Earth’s surface. Any rock may weather but what will this one
weather to? Limestones may easily and entirely dissolve to ions and saltiness in the sea
(caves anyone?) but shales, schists or granites tend to mechanically weather to rock
fragments. What kind of residual particles will each rock type make for future
sediments? Quartz will last and feldspar might for a while. Most ferromagnesian
minerals react to clays, iron oxides (red dirt) & dissolved salts. Sediments are low
pressure rocks deposited on top of the earth’s surface and only shallowly buried if at all.
As a result they have abundant open pore spaces and are often filled with economically
important resources like ground water, petroleum or natural gas.
Partial Melting: All igneous rocks originated by partial melting, moved upwards
in the crust by buoyancy and flow and cooled to form solid rocks. The mantle peridotite
partially melts to make basalt at about 1250°C. The gabbro or amphibolite lower crust
can partially melt to make rhyolite at about 1000°C. Pure quartz doesn’t melt until
1700°C. Calcite usually doesn’t survive to get hot enough to melt because it decrepitates
to carbon dioxide (CO2 (g) ) and Calcium Oxide (CaO) or another calcium bearing mineral
at temperatures above 750°C. Most rocks can partially melt if they get hot enough but
what kind of melts could each particular rock generate? Be specific.
Metamorphism: Any rock may get strained and re-crystallized by changes of
pressure, temperature, stresses and fluids that collectively add up to metamorphism.
Judging from the minerals already present what new minerals would form from the bulk
composition of each rock pictured or in the specimens provided? Clays may recrystallize into micas and aluminosilicate minerals (kyanite, sillimanite, andalusite). Pure
quartz or calcite just stay as quartz or calcite but a marly sediment containing calcite,
quartz and clays make calcium rich silicate rocks or coarse grained skarns with minerals
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like tremolite, actinolite, diopside or grossularite garnet. Shales may metamorphose into
schists or gneisses. Granites may metamorphose into gneisses. Volcanic rocks may
metamorphose into greenstones (low temperatures and pressures) or blueschists (low
temperatures and very high pressures).
B) Seven unnamed rock specimens are pictured in figures 4.5 to 4.11 on pages 96-97.
Examine these photos carefully and find real rock specimens like them if you can in the
lab to help your observations and descriptions. Fill out the table provided on p. 100,
being careful to note which rock description goes on each line! In column 1 list at least 2
specific terms for textures, minerals, fossils, cements. In column 2 instead of just putting
down igneous, sedimentary or metamorphic, I have helped you in the right direction by
doing this for you with the I, S, M in the corner. However I’d like you to name the rock.
In the 3rd column, be specific as to the rock’s conditions of formation or original
geological setting. Petrologists do this when the look at rocks to see not only what is
before their eyes, but also they interpret the environment that created it. Finally in the last
column, put 1 realistic example of a specific sedimentary, metamorphic and igneous
process that could befall each rock in the rock cycle. For example using some of the
reference pictures in Fig 4.3 on p 92, the table might look like this: (42)
Sample# Rock Properties
Classification/Name Origin/Formation
Future Changes
A
IGN-Obsidian
Clay, salt
Glassy fractured
devitrified and
discoloured
Quenched fast
from subaerial
volcano
Schist
Remelt
E
I
Crystalline, non
foliated, calcite
MET-Marble
Fine grained leaf SED-Redbed
fossil hematite
Fossiliferous
cement
Siltstone
Recrystallized
limestone
convergent marg
Salts
Clastic lacustrine
or riverine on
land
Mud & salts
Marble
Schist
Rhyolite melt
Activity 4.2: Real Rock Samples and the Rock Cycle
7 real hand specimens are provided of typical igneous, metamorphic and sedimentary
rocks. Some of these are blocky or angular hand specimens broken from outcrops and
some are cut and polished slabs. The polished slabs help you to see textures and shapes
along the random plane of the cut. Freshly broken surfaces reveal mineral crystal faces or
grain shapes and the rock’s true colour. Long exposed weathered surfaces reveal how the
rock weathers and how it falls apart, along joints or bedding planes. It also reveal
weathering or secondary minerals eg. Sulfates or oxy-hydroxides for primary sulfides.
Examine these rocks carefully and other similar real rock specimens like them in the
Ward’s rock sample kits, to help your observations, descriptions and interpretations. Fill
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out the table provided on p. 101 labeled Activity 4.2, again being careful to note which
rock description goes on each line! Rocks A, B & C are all Sedimentary, D and E are
Igneous and F & G are Metamorphic. Fill in the columns as you did for the rock photos,
again practicing your new rock texture and mineral vocabulary. In column 1 list at least 2
specific terms for textures, minerals, fossils, cements. In column 2 name the rock. In the
3rd column, be specific as to the rock’s conditions of formation or original geological
setting. Petrologists do this when the look at rocks to see not only what is before their
eyes, but also they interpret the environment that created it. Finally in the last column, put
1 realistic example of a specific sedimentary, metamorphic and igneous process that
could befall each rock in the rock cycle. (42)
Part 4C:
Drawing Hand Specimens and Thin Sections
Draw and label 3 hand specimens from the A-F rocks provided. Do 1 each of an
Igneous, Metamorphic and sedimentary specimen. With each Drawing include a scale bar
showing how big 5 cm is compared to the rock, textures, mineral grains fossils etc. that
you show. Don’t just write X2 as this changes under reproduction, while a scale bar
remains true! Label each mineral or texture you draw. Do this also for 3 thin sections
under the petrographic microscope. (30)
Hand
Specimen No. _
Hand
Specimen No. _
Hand
Specimen No. _
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Thin Section
No. ______
Thin Section
No. ______
Thin Section
No. ______
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Include Xeroxes or scans of rock cycle p 99 and tables p 100, 101 out of AGI MANUAL
EDITION 9
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