HNRT 227
Laboratory Experiment #8 with Ms. Crowell
FALL 2015
The Rocks of Earth and the Surface of Mars
Purpose: To understand the rocks of terrestrial planets and how they are formed, and to
interpret and analyze the surface of planets and what that teaches us about the conditions
that exist today and may have existed eons ago.
Earth Rocks Introduction
Minerals are defined as naturally occurring, inorganic, solids with a definite chemical
composition and a regular, internal crystalline structure. The keys to this definition are
the chemical composition and the crystalline structure. Different chemical compositions
result in different minerals. A good example is the mineral plagioclase. Plagioclase is a
member of the feldspar group, but there is more than one type of plagioclase. Albite and
anorthite are two examples. Albite has a chemical composition of NaAlSi3O8, while
anorthite's chemical compositon is CaAl2Si2O8. Very similar, but still different, therefore
two different minerals.
Different crystalline structures, or how the atoms and molecules are arranged, result in
different minerals. A good example is diamond and graphite. Both minerals are composed
of carbon (C). The same chemical composition, but two different crystalline structures therefore, two different minerals.
Determination of the actual chemical composition and crytalline structure of a mineral is
difficult without the proper equipment. In an introductory level lab it is impossible for us
to determine these two aspects of a mineral. Fortunately, these two aspects determine a
mineral's physical properties. How the atoms and molecules are arranged and the strength
of the bonding between the atoms result in different physical properties for different
minerals. While many minerals share common physical properties, when all of a mineral's
physical properties are examined, it often results in a unique set of physical properties
which can be used to identify the mineral.
Below you will find a chart which defines the physical properties and provides the means
for determining the physical property of a mineral sample. These definitions and methods
are simplified. Consult your lab manual for detailed discussion.
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Mineral Physical Properties Chart
PHYS
ICAL
Definition*
PROP
ERTY
Breakage of a mineral along
Cleava
planes of weakness in the
ge
crystral structure.
Visible light spectrum
Color radiation reflected from a
mineral.
Crysta Geometric shape of a crystal
l Form or mineral.
Breakage of a mineral, not
Fractu
along planes of weakness in
re
the crystral structure.
Hardn Resistance to scratching or
ess
abrasion.
Testing Method
Examine the mineral for areas where the mineral is broken. Look for areas
where the light reflects from planar surfaces. This can be easily confused with
a crystal face and is the most difficult properties for students to master.
Look at the sample and determine its color - white, black, green, clear, etc.
Examine and describe the geometric shape of the mineral - cubic, hexagonal,
etc. Not commonly seen in most introductory lab samples.
Examine the mineral for areas where the mineral is broken. Describe the
breakage as either irregular or conchoidal (has the appearance of broken glass)
Use minerals of known hardness from the Mohs Hardness Kits. Scratch the
unknown mineral with a known hardness to determine which mineral is harder.
Continue doing this with harder or softer minerals from the kit until the
hardness is determined.
Look at the sample to determine if the mineral is metallic in appearance (looks
like a chunk of metal) or non-metallic (doesn't look like a chunk of metal).
Character of the light
reflected by a mineral.
Electromagnetic force
Magne
generated by an object or
Use a magnet to determine if the magnet is attracted to the sample.
tism
electrical field.
Reacti Chemical interaction of
Place one small drop of HCl on a sample a watch for a reaction - effervesces
on to hydrochloric acid and
(bubbles).
HCl calcium carbonate (CaCO3).
Specifi
Ratio of the mass of a
c
Generally not determined in an introductory lab. Look this information up in
mineral to the mass of an
Gravit
your lab manual once the mineral has been identified.
equal volume of water.
y
Color of the mineral when it Grind a small amount of a mineral into a powder on a porcelain streak plate
Streak
is powdered.
and determine the color of the powder.
Nerve ending reaction in the
Lick the mineral. (not recommended in an introductory lab - you don't know
Taste tongue to different
who has handled or licked the sample before you).
chemicals.
Other
Requires special equipment such as a UV lamp and geiger counter. These are
Proper Fluorescence, Radioactivity
not commonly tested for in an introductory lab.
ties
* Definitions simplified or modified from Bates, R.L. and J.A. Jackson (eds.), 1987, Glossary of Geology.
American Geological Institute, Alexandria, VA, 788 p.
Luster
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Igneous rocks are rocks that solidify from molten material (magma). Cooling of the
magma can occur beneath the surface (plutonic) or on the surface (volcanic). Igneous
rocks can be identified by the determination of the composition and texture of the rock.
Once these two characteristics have been identified, the Igneous Rock Identification chart
can be used to help identify the rock name.
Igneous Rock Identification Chart
COMPOSITION
\\\\\\\\\\\\\\\\
Felsic
Intermediate
Mafic
Granite Pegmatite
Diorite Pegmatite
Gabbro Pegmatite
Ultramafic
TEXTURE\\\\\\\
Pegmatitic
Phaneritic
Aphanitic
Porphyritic
Glassy
Vesicular
Pyroclastic
Granite
Rhyolite
Rhyolite
Diorite
Andesite
Andesite
Obsidian
Pumice
Volcanic Tuff
Gabbro
Basalt
Basalt
Basaltic Glass
Scoria
Dunite
Composition of igneous rocks is properly identified by determination of the rock’s
chemical composition. This, however, requires chemical equipment and apparatus that is
unavailable in this lab. Fortunately determination of the exact chemical composition is
not necessary. Color is often an indicator of the composition of a rock or mineral and can
be effectively used to identify the composition of most igneous rocks. Light colors,
including white, light gray, tan and pink, indicate a felsic composition. Felsic
compositions are rich in silica (SiO2). Dark colors, such as black and dark brown,
indicate a mafic or ultramafic composition. Mafic compositions are poor in silica, but
rich in iron (Fe) and magnesium (Mg). Intermediate compositions have an intermediate
color, often gray or consisting of equal parts of dark and light mineral. Beware that even
though an igneous rock may have a felsic composition (light color), the rock can contain
dark colored minerals. Mafic rocks may contain light colored minerals as well. As
mentioned above, the composition of most igneous rocks can be identified using this
system, formally known as the Color Index. However, there are exceptions. The two
most notable are obsidian and dunite. Obsidian is volcanic glass which erupts as a lava
flow. Most obsidian is felsic in composition, yet typically it will have a very dark color
(dark brown to black). Dunite has an ultramafic composition yet is apple green to
yellowish green in color. Dunite is composed almost entirely of the mineral olivine
which usually contains both iron and magnesium.
The texture of an igneous rock does not refer to the roughness or smoothness of the
surface. Textures are based primarily on crystal size. Pegmatitic texture is composed of
very large crystals (larger than 2-3 cm). Phaneritic texture is composed of crystals that
are large enough to see but smaller than pegmatitic texture, and the entire rock is
composed of crystals. Aphanitic texture is a fine grained texture but the crystals are too
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small to see. Porphyritic texture is composed of crystals of two different sizes. Typically
the large crystals (phenocrysts) are visible while the smaller crystal are not (referred to as
groundmass). Glassy texture is the most readily recognized. The rock is composed
entirely of glass. Few, if any, crystals will be visible. Vesicular texture is formed when
lava solidifies before gases are able to escape. The result is a "bubbly" appearance.
Lastly, pyroclastic texture is composed of volcanic fragments. These fragments or clasts
can be very fine (ash) or coarse (lapilli) or very coarse (bombs and blocks).
Sedimentary rocks are rocks composed of sediment. Sediment is deposited in a number
of environments of deposition, by both moving air and moving water. Sedimentary rock
identification is primarily based on composition. Texture will still be used but in a
different sense than for igneous rocks.
Texture of sedimentary rocks in this lab will be taken to indicate origin or type of
sediment found in the rock. Three types of sedimentary rock "texture" are clastic,
chemical, and biologic.
Clastic sedimentary rocks contain clasts. These are fragments or pieces of rock or
minerals. The composition of clastic sedimentary rocks is divided into three types clay/silt, sand and gravel. Clay and silt are less than 1/256 mm. These are not visible to
the unaided eye. Sand is clasts between 1/16 and 2 mm in size, and gravel is greater than
2 mm.
Chemical sedimentary rocks are identified by identifying the mineral from which they are
composed. Four minerals that need to be identified are quartz, halite, gypsum and calcite.
Quartz has a hardness of 7 and is very difficult to scratch, even with a good quality knife
blade. Gypsum is relatively soft (Hardness =2) and can be scratched easily with a
fingernail. Halite is common table salt and is most easily identified by taste. However,
this is not a sensible practice in a large lab with many different people handling the
samples. Halite has a hardness of 2.5 and cannot be scratched by a fingernail (unpolished
fingernail). Calcite readily reacts with a small drop of HCl.
Biologic sedimentary rocks are which form as the result of the accumulation of organic
material or biologic activity. Coal is usually obvious to most students even though few
people seem to have ever actually examined it up close. The dark brown to black color is
the most obvious characteristic. Coquina and limestone are both composed of calcite.
Coquina is composed almost entirely of shell or fossil fragments. Limestone may or may
not contain fossils. Both will react to HCl. Limestone containing fossils is referred to as
fossiliferous limestone.
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Sedimentary Rock Identification Chart
TEXTURE
Clastic
Chemical
Biologic
GRAIN SIZE
2 mm
1/16 - 2 mm
<1/16 mm
1/16 mm
COMPOSITION
rock fragments, quartz, feldspar
quartz, feldspar
quartz, clay minerals
feldspar, quartz
calcite
silica (quartz)
gypsum
halite
organic material, plant fragments
calcite, shell and skeletal fragments
calcite with some fossils
ROCK NAME
Conglomerate
Sandstone
Mudstone
Arkose
Limestone
Chert
Rock Gypsum
Rock Salt
Bituminous Coal
Coquina
Fossiliferous Limestone
Metamorphic rocks are rocks that have undergone a change from their original form due
to changes in temperature, pressure or chemical alteration. The classification of
metamorphic rocks is based on the minerals that are present and the temperature and
pressure at which these minerals form. Determination of this information is not easily
accomplished in this lab. Therefore, a simplified system is used based on texture and
composition.
Texture is divided into two groups. Foliated textures show a distinct planar character.
This means that the minerals in the rock are all aligned with each other. This planar
character can be flat like a piece of slate or folded. Non-foliated textures have minerals
that are not aligned. Essentially, the minerals are randomly oriented.
Foliated textures show four types of foliation. Slaty cleavage is composed of platy
minerals that are too small to see. Typically, these rocks split along parallel, planar
surfaces. Phyllitic foliation is composed of platy minerals that are slightly larger than
those found in slaty cleavage, but generally are still too small to see with the unaided eye.
The larger size gives the foliation a slighly shiny appearance. Schistose foliation is
composed of larger minerals that are visible to the unaided eye. Platy minerals tend to
dominate. Gneissic banding is the easiest of the foliations to recognize. It is composed of
alternating bands of dark and light minerals.
Non-foliated textures are identified by their lack of planar character. Further
identification of non-foliated rocks is dependent on the composition of the minerals or
components in the rock. Anthracite coal is similar to bituminous coal. Both are black in
color, and is composed of carbon. Anthracite coal is generally shiny in appearance and
breaks with a conchoidal fracture (broken glass also shows this type of fracture).
Metaconglomerate is composed of pebbles and gravel that have been flattened due to
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directed pressure. Quartzite is composed of quartz sand grains. Quartz has a hardness of
7, which makes it difficult to scratch. Marble is composed of calcite and will readily
react to a small drop of HCl.
Metamorphic Rock Identification Chart
TEXTUR
FOLIATION COMPOSITION
E
slaty
mica
quartz, mica,
phyllitic
chlorite
schistose
mica, quartz
Foliated
amphibole,
schistose
plagioclase
gneissic
feldspar, mica,
banding
quartz
ROCK
NAME
Slate
Regional
Mudstone
Phyllite
Regional
Slate
Basalt or
Gabbro
Schist
Regional
carbon
NonFoliated
Regional
PARENT
ROCK
Mudstone
TYPE
quartz, rock
fragments
calcite
quartz
Regional
Schist
Contact or
Regional
Contact or
Regional
Contact or
Regional
Contact or
Regional
Bituminous
Coal
Amphibolite
Gneiss
Anthracite
Coal
Metaconglom
Conglomerate
erate
Limestone
Marble
Sandstone
Quartzite
Mars Surface Introduction
In many ways Mars is similar to Earth. The same geologic processes that shape Earth, i.e.,
erosion, impact cratering, tectonism, and volcanism, have left their mark on Mars.
Volcanism has produced vast lava flows, broad shield volcanoes, and plains of volcanic
material. Mars has some of the largest volcanoes in the solar system, including Olympus
Mons, a massive volcano many times larger than the Island of Hawaii. Olympus Mons is
only one of four huge volcanoes in a 3000 km-wide region called Tharsis. These
volcanoes erupted repeatedly over many millions of years, growing higher with each lava
flow. Enormous collapse calderas are found on the summits of each of the volcanoes.
Erosion is the dominant geologic process acting on Mars today. Mass movement is the
displacement of material by landslides or slumping through the action of gravity. Aeolian
(wind) activity is also a continuing process of erosion. Sand and dust particles carried by
the wind form dunes and windstreaks. Although temperatures below freezing and low
atmospheric pressures do not allow liquid water on the surface of Mars today, erosion
processes involving running water were important on Mars in the past. Valley systems cut
through many of the cratered terrains of Mars and have characteristics analogous to
water-cut valleys on Earth.
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A mystery concerning water on Mars is "Where did it go?" Some water probably seeped
into the ground and is frozen there today as ice, and some likely escaped into space over
time. Moreover, the polar caps contain some water ice. Mars, like the Earth, has seasons.
The polar caps shrink during local summer and grow during local winter.
Although Mars does not have plate tectonics like the Earth, there are many tectonic
features that show its surface has been deformed. Stresses can be caused by subsurface
uplift or by the addition of mass (such as lava flows) that weigh down an area.
Extensional stresses have led to the formation of great valleys such as Valles Marineris,
the longest canyon system in the solar system. As on the Moon, Mercury, Venus, and
most of the outer planet satellites, impact craters are found on the surface of Mars. Craters
can be used to determine the relative ages of Martian surface materials; in general, older
surfaces have craters which are more numerous, larger, and more degraded than those on
young surfaces. Moreover, the principles of superposition and cross-cutting relations
indicate that a feature which at least partly covers another feature is the younger. Thus, if
a valley cuts through a crater, the crater must be older. Individual craters are degraded or
destroyed over time by erosional processes and further cratering. Therefore, crisp craters
with upraised rims and steep sides are young, while less distinct and eroded craters with
partial rims are probably older. Through a combination of these principles, the relative
ages of geologic features can be determined, and a sequence of geologic events
developed.
This lab is an adaptation of an adaptation by Richard Harwood based upon the original
NASA resource: A Teacher's Guide with Activities in Physical and Earth Sciences
for Planetary Geology,: National Aeronautics and Space Administration, 1998, EG1998-03-109, p. 238.
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Procedures and Lab Questions to be Turned In: Part 1
Olympus Mons is a shield volcano 600 km in diameter, towering 25 km above the
surrounding plain. Around its base is a steep cliff as high as 6 km. It has a summit caldera
some 80 km wide.
Figure 1. Martian shield volcano, Olympus Mons. (Viking MDIM mosaic 211-5360)
1. Examine the caldera (labeled A) and describe its shape.
2. Determine and record the diameter of the caldera structure (include the over all caldera
structure in this measurement).
3. Measure and record the diameter of Olympus Mons. Measure and record the east-west
and north-south diameters.
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4. Suggest some ways in which the scarp around Olympus Mons might have formed.
5. Do you think the surface of Olympus Mons is geologically old or young, compared to
the surface of the Moon? Explain your answer.
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Procedures and Questions: Part 2
Ius Chasma is part of the western end of Valles Marineris, the largest Martian canyon.
Smaller valleys join the main east-west chasm.
Figure 2. Ius Chasma, part of the Valles Marineris system. (Viking image 645A57)
6. Using the following picture
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draw a box around the area that is shown in Figure 2.
7. Compare the size of Ius Chasma and its tributaries to the size of the Grand Canyon of
Arizona (approximate length=175 km and maximum width=29km). Measure and record
the width of the Ius Chasma. Which is larger, and by how much?
8. Which of the four geologic processes might be responsible for the formation of Ius
Chasma? Explain why you believe this is so.
Procedures and Questions: Part 3
Now we examine some Valleys west of Chryse Planitia. Similar to some river systems on
Earth, these Martian channels have a branching pattern.
Figure 3. Valleys on western Chryse Planitia near Viking 1 site. (Viking mosaic P-17698)
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9. In what direction did the water flow? Explain why you believe this is so.
10. Based on the number and morphology of craters, is this a relatively old or young
region of Mars? Explain why you believe the way you do.
11. Are the craters you observe older or younger than the valleys? Explain your answer.
[Hint: use the principle of cross-cutting relations to justify your answer.]
12. What is the diameter of the large crater towards the bottom of the image?
Procedures and Questions: Part 4
The Hesperia region in the southern hemisphere consists of cratered plains which have
been modified by aeolian processes. Wind-produced features, called bright windstreaks,
are associated with many craters.
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Figure 4. Hesperia Planum, showing bright windstreaks associated with some of the craters. Location: 24ºS,
245ºW. (Viking MDIM Volume 4)
13. Describe the appearance and orientation of the windstreaks.
14. If windstreaks are dust deposits formed downwind from the craters, what wind
direction is indicated here? Explain your answer. (Hint: remember that wind direction
refers to the direction from which the wind blows.)
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Procedures and Questions: Part 5
Finally, let's examine Apollinaris Patera and surrounding region. All four geologic
processes can act to shape a planetary landscape. For the following, you will use the
knowledge from previous questions to identify Martian landforms and describe the
geologic processes that created them.
Figure 5. Apollinaris Patera and surrounding region centered at 10ºS, 190ºW. (Viking MDIM Volume 4)
15. Compare Apollinaris Patera (marked A on Figure 5) to Olympus Mons (Figure 1).
Explain their similarities and their differences.
16. Determine and record the diameter of Apollinaris Patera?
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17. What process do you think formed Apollinaris Patera? Explain how you can tell.
18. What process do you think formed Reuyl crater (marked B on Figure 5)? Justify your
answer.
19. Ma'adim Vallis is the channel in the southeast part of the photograph, marked C.
Which of the four processes do you think formed Ma'adim Vallis? Justify your answer.
20. Consider the relationship between Ma'adim Vallis and Gusev, the 160 km diameter
crater marked D. Explain what could be the origin of the material that comprises the
floor of Gusev? (Hint: the region slopes to the north.)
21. Based on your observations, what is the probable order of occurrence of A, B, C, and
D in Figure 5 (i.e., which came first, second, third, last)? Give evidence for your answer.
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