Name(s): _____________________________________________________
For Busch & Tasa 9th ed. 2013
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 finecrystalline 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 ring-of –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
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)
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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 re-crystallize 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 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
Quenched fast
from subaerial
2
discoloured
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 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-G 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, label 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.
(15)
3
Hand
Specimen
Letter _____
Hand
Specimen
Letter _____
Hand
Specimen
Letter _____
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4.1.A-1) On the diagram above label each process that creates a sedimentary rock with the same colour
and use acontrasting colour for the other processes tat generate igneous or metamorphic rocks. Every
line and arrow on the diagram should be coloured in (11 points)
4.1.A-2) In the Table above put a coloured X under each column if there are rocks for which this is an
essential attribute. (Hint you’ll have a total of 14 X’s if you do this correctly!) (14 points)
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