Download Introduction to Minerals and Igneous Rocks

INTRODUCTION TO GEOLOGY HONORS
EXERCISE TWO (LAB)
INTRODUCTION TO MINERALS AND IGNEOUS ROCKS
Following the introductory lecture, utilize the mineral and rock samples that you have been given
to answer the questions below.
Mineral Characteristics
1. List (by sample number) three minerals that have a metallic luster.
2. List (by sample number) three minerals that have a glassy luster.
3.
Determine the relative hardness of the following samples: 3, 7 and 21. List them in
order from hardest to least hardest. Remember, if a harder substance will scratch a softer
substance.
4. Compare the hardness of samples 3, 7, and 21 to glass, a copper penny and your
fingernail. List the three samples and glass, copper and a fingernail in order of
decreasing hardness.
5. The hardness of a mineral can be communicated as a number by using the Moh’s
hardness scale. This scale goes from 1 to 10, and on it glass has a hardness of 5.5, copper
is 3 and a fingernail is 2.5. Estimate the numerical Moh’s scale hardness of samples 3, 7
and 21 by comparison with glass, copper and fingernail.
6. Many minerals have the property of cleavage, which is a tendency to break along fairly
straight planes in certain directions. Break a piece of the calcite that’s in the small
bucket/cup.
a. Does this mineral have cleavage?
b. In how many different directions does this mineral tend to break?
7. Density: which is more dense, sample 16 (pyrite, made of iron and sulfur) or 17 (halite,
made of sodium and chlorine)?
Crystallinity and the Internal ordered arrangements of atoms in minerals
8. Minerals are crystalline, which means that the atoms in them are arranged in a regular,
repeating pattern. This pattern is often reflected in properties of minerals. For example,
GEOL 101H Exercise 2, Minerals and Igneous Rocks
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in halite (#17), the sodium and chlorine atoms are arranged in a cubic (“square”) pattern
that is reflected in halite’s strong tendency to break into cubes.
a. Examine the other samples in your mineral kit and find mineral galena (lead
sulfide) that has the same tendency to break into cubes as halite does (hint, it has
a metallic luster, as do many sulfide minerals). Give the sample’s number.
b. Examine sample 3. It did not break into a 6-sided shape, it grew naturally into
that shape. Can you make any guesses about the pattern of the arrangement of
the atoms in this mineral based on its shape?
The Common Igneous Minerals
9. Take the following samples out of your mineral kit: 1, 2, 3, 5, 6, 41, 42, 43. These are the
common igneous minerals. The names of the minerals and some of their characteristics
are listed on an attached page.
a. Match the numbers of the mineral samples to their names.
b. Divide them into two groups based on some characteristic(s) of them that you
think may be important to understanding their formation. List the two groups
below, and briefly explain your rational for creating the two groups.
c. Divide them into two groups again. Talk to Brian or Mike for advice on how to
divide them this time. List your two groups and your rational for creating them.
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So far, you have mostly examined minerals. In the following part of the lab you will be working
with igneous rocks.
10. What are igneous rocks – that is, what do all igneous rocks have in common that
distinguishes them from sedimentary and metamorphic rocks?
11. Remove the following rock samples from your kit: 21, 22, 23, 24, 25, 26.
a. Divide them into two groups based on some characteristic(s) that you think may
reflect how they formed or some important aspect of the rocks. List your two
groups and your rational for creating them below.
b. Now divide them into two different groups based on some other characteristic
that you think may reflect how they formed or some important aspect of the
rocks. List your two groups and your rational for creating them below.
At this point you are ready for the second part of today’s lecture. If you have extra time,
experiment with some of the other minerals in your kit.
12. Now you are ready to officially categorize your samples of igneous rock based on
whether they are intrusive or extrusive and whether they are mafic, intermediate or felsic.
Complete the following chart with the correct sample numbers and rock names.
Felsic
Intermediate
Mafic
Extrusive
Ultramafic
Komatiite
Intrusive
Peridotite
13. Using the attached map and your knowledge of the plate tectonic settings in which the
different types of igneous rocks tend to form, for each rock sample list (by number from
the map) places where it might have formed. What popular tropical vacation spot is a
good place to find lots of rock like sample 25?
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The Common Igneous Minerals (add your own notes)
Biotite – brown, forms distinctive sheets (like muscovite but dark brown in color)
Hornblende – Dark brown, elongate crystals that are diamond – shaped perpendicular to long
direction, hardness 5 to 6.
Muscovite – clear/silver, forms distinctive sheets (like biotite but clear to silver in color)
Olivine – light to very dark green, stubby to roundish crystals, usually sand to pebble sized,
glassy, hardness 6.5 to 7
Plagioclase feldspar – white to very dark-clear-gray (even when dark has a sort of see-through
quality), good cleavage (forms little mirror-like surfaces when in rocks).
Potassium feldspar (orthoclase) – white to pink orange color, good cleavage (forms little
mirror-like surfaces when in rocks), hardness 6.
Pyroxene – Gray-green to brown, blocky/stubby shaped crystals, hardness 5 to 6.
Quartz – clear to gray, glassy/oily luster, hardness 7.5. Often appears clear in large crystals,
milky white in fine-grained masses, clear-gray in rocks.
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