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Physical Geology 101 Lab #3

MINERALS – Properties, Classification and Identification

 

INTRODUCTION:  The purpose of this lab is to learn the characteristics of minerals, and to identify minerals in hand samples from their physical properties.  You will become familiar with a number of common rock forming minerals and several other minerals that are less common, but are important because they are the principle sources of economically important materials (such as iron and copper).   The objective of this lab is for the student to be able to identify major rock-forming minerals hand specimens by determining their physical properties.

 

PRELAB SECTION – To be completed before the lab meeting (First two pages)

 

I. MINERAL DEFINED

1. A mineral is defined by five attributes; a substance must possess these five attributes to be labeled a mineral.  Directions:  List the five attributes for a mineral as noted in your lab book.  See page 47 in your lab book.

 

            1. ________________________________

            2. ________________________________

            3. ________________________________

            4. ________________________________

            5. ________________________________

 

2.  Does coal or natural glass (obsidian) meet this definition of a mineral?  Justify your answer.

 

      Coal – Yes or  No? Why?_______________________________________________________

 

      Natural glass  - Yes or  No? Why?________________________________________________

 

II. HARDNESS:  Some minerals are harder than others.  Each mineral has a specific hardness (or at least a restricted range). You can test this for yourself because harder minerals will scratch softer minerals.  Choose two mineral samples and try it yourself.  A mineral's hardness sometimes determines its usefulness as an economic material. Cutting, grinding and polishing tools typically require abrasives with a specific hardness, depending on the material being worked on.  Hard minerals, such as garnet, corundum, and diamond, are used as abrasives for working with hard stone or metals.  Some hard minerals are also attractive as gemstones, due in part to their resistance to scratching.  Soft minerals such as calcite are used as mild abrasives and polishes where the working material is more delicate.

 

1. Question:  Why would a soft mineral be a poor choice for a gem, even if it were very attractive?

 

 

 

2.  Soft minerals are sometimes used as mild abrasives if the working material is also soft. 

     Question: Can you think of a mineral that you probably use every day as a mild abrasive/polish?

 

 

 

 3. Questions: Why does it have to be soft?  What would happen if it were replaced with a hard abrasive?

 

4. A mineral hardness scale, called MOHS HARDNESS SCALE, uses 10 specific minerals - each with a unique and different hardness (1 to 10) - for comparison with other minerals.  The 10 minerals are arranged in order of hardness and numbered from one to ten on the scale of hardness.

 Directions: List the 10 Mohs Hardness minerals below. (Info found on page 53 in your lab book)

 

   Soft minerals:   1) _______________    2) _______________   3)________________   

                                          4)___________________    5)__________________

  Hard minerals:    6)_________________   7)__________________   8)__________________   

                                           9)____________________    10) ___________________

 

Note that the 9 specimens in your hardness kit box are the first 9 minerals of the Mohs scale.

 

 5. Question: Guess why the #10 hardness mineral is missing from the hardness kit.   

 

 

Identifying Minerals by Hardness: When geologists need to identify minerals in the field they frequently carry a mineral hardness kit to test field samples for mineral hardness.  However, most of us do not walk around with a hardness kit for checking mineral hardness, so it is difficult to make a hardness comparison of minerals when out in the field.  So, we can use more common items in place of the Mohs minerals. 

 

6. What is hardness for these common items below?  (You will find this on page 53 in your lab book)

 

     Streak plate =  _____  Glass plate =  ______    Knife blade = _____

 

          Iron (carpentry) nail = ______Copper penny = _____     Fingernail = _____

 

Note that specimens equal to or harder than feldspar (H = 6) are considered "HARD".  A “Hard” mineral will scratch glass (H = 5.5).   Specimens softer than flourite (H = 4) are considered "SOFT".

 

Questions:

 

7.    Which of the above test item(s) appears to the BEST hardness testing tool for identifying the

     "HARD" minerals from the softer minerals?

                                                                                     Answer______________________________ .

 

8.   Which Mohs minerals is the hardest that you can scratch with your thumbnail? ______________

 

10.  Which Mohs minerals is the hardest that you can scratch with a carpenters nail? ____________

 

12.  Which Mohs minerals is the softest mineral that will scratch a glass plate? _______________

 

 

 

 

IN-LAB SECTION –To be completed during lab

 

III. LUSTER:  The luster of a material refers to the way it reflects light.  Is it shiny like glass, metallic like metal, waxy like a candle, pearly like pearl, dull, etc? The various mineral lusters are listed and described in the lab book.  Each mineral has a characteristic luster.  A single mineral type may have several lusters, depending on the sample.  The most preliminary criterion for identifying a mineral is whether a mineral has a metallic versus nonmetallic luster.  Note that many metal-bearing ores have a metallic luster, whereas, all the silicate and carbonate minerals have a non-metallic luster.

 Directions:  Classify all 30 mineral samples in the box collection according to their luster:

 

Metallic Luster

1.  Samples #’s _____________________________________________  have a metallic luster.

 

Nonmetallic Lusters

2.  Sample #’s  _____________________________________________have a nonmetallic luster.

 

IV. COLOR and CLARITY:  The color of a mineral is usually helpful in determining it identity. However, quite a few minerals have a variety of color, depending on the type of chemical impurities.

One useful way to use color for mineral identification is to divide minerals into two color types: light-colored versus dark-colored.   The secondary use of color is then to defined the actual hue, such as white, red, orange, yellow, green, blue, violet, gray, black, and all the tonal variations.

 

  Directions: Classify (divide) the 30 minerals according to whether they are light- or dark-colored:

 

Samples#  _________________________________________________ are light-colored.

 

Samples# __________________________________________________ are dark-colored

 

V. FRACTURE:  Minerals that break along curved or rough, uneven surfaces are said to fracture rather than cleave.  Many minerals fracture in some directions and cleave in others.  For example: Examine Orthoclase Feldspar.  It cleaves in two directions, but fractures in the third.  Examine Muscovite Mica.  It cleaves in one plane, but fractures in any other direction.  In contrast, Quartz only has fracture surfaces, with no observable cleavage.  Note: do not confuse the six-sided crystal-form faces of quartz for cleavage faces.

 

1.  Name another mineral that cleaves in two directions, but fractures in the third. _______________

 

2.  Name another mineral that cleaves in one direction, but fractures in others. _________________

 

3. Name another mineral that has no cleavage - only fracture  _________________

 

Look at your quartz sample.  If it has been broken you will see that it did not break along a crystal face.  Do not confuse the smooth, flat, six-sided form in which a crystal grows with a cleavage face.  Quartz grows with no cleavage.  Minerals that break leaving a rough surface are said to have an IRREGULAR FRACTURE.  Minerals that fracture in a smooth, curved surface rather than a rough, uneven, blocky surface are said to exhibit CONCHOIDAL FRACTURE. 

 

4. What kind of fracture does your Quartz sample(s) show? ______________________________

 

Quartz, Chalcedony, Jasper, and Chert are all forms of pure silica with similar physical properties. Silica is the name for the chemical compound SiO2.  Quartz and chalcedony are minerals; jasper and chert are rock names.

 

 

VI. CLEAVAGE:  Some minerals break along smooth, flat, parallel surfaces called CLEAVAGE PLANES.  These smooth, flat, shiny surfaces are planes of weakness in the mineral crystal.  When a mineral "cleaves" or breaks into an easily recognized shape it will help us to recognize the mineral.   Cleavage of a mineral is described in terms of, the number of cleavage planes, the quality (perfect, good, poor), and the angles between the cleavage planes.  For example the cleavage of the mica minerals, like biotite and muscovite, have one single perfect cleavage plane, as you can cleave the mineral into thin flat “plates” or “sheets”.   Check for mineral cleavage by turning the sample back and forth, as you look for patches of bright reflected light emitted from mineral cleavage surfaces.  If cleavage is present, then determine how many co-planar sets of cleavage are present.

 

Directions: Carefully examine the following mineral samples.  Determine each mineral’s unique cleavage.  Check your determination with the cleavage listed for that mineral in the mineral database in your lab book (pages 66 to 70). Draw a line connecting the mineral(s) to their correct type of cleavage character.

 

    Mineral                                                                                  Type of Cleavage

 

1. Feldspar and Pyroxene                                                    no cleavage/ only fracture

2. Magnetite and Pyrite -                                                1 - perfect  

3. Galena and Halite                                                              2 - good; @ 90

4. Calcite and Dolomite -                                                       2 - good @ 56/124

5.  Gypsum –                                                                                3 – (1-good; 2-poor) @ 90

6.  Biotite and Muscovite –                                                     3 - perfect @ 90 

7.  Quartz and Olivine -                                                           3 - perfect @ 60/120

8.  Fluorite -                                                                             4 – perfect

9.  Amphibole –                                                              

VII. CARBONATE MINERALS:  The minerals Calcite (CaCO3), and Dolomite (Mg,Ca)2CO3 are very common in sedimentary and metamorphic rocks like limestone and marble, respectively. Three physical properties help set these minerals apart from others that might “look” like them: 1) hardness of three; 2) three sets of cleavage at 60/120 degrees; and 3) reaction to dilute HCl acid (the acid test)

THE ACID TEST: The expression "The Acid Test" has become a figure of speech in the English language.  It indicates certainty.  This expression comes from the test geologists use for the mineral Calcite (CaCO3), and Dolomite (Mg,Ca)2CO3.

 

Directions: Put a drop of dilute hydrochloric acid (HCl) on your calcite sample; observe the results:

 

1. Describe the result of the acid test.  What do you think is happening?

 

 

2. Chalk consists of very tiny shells made of calcite.  Do the acid test on a piece of chalk.  Results?

 

 

3. Kaolinite looks like chalk but is actually clay.  Give it the acid test.  Is Kaolinite a carbonate? _____

 

VIII. The SILICATE MINERAL GROUP: Silicates make up the vast majority of rock-forming minerals (by volume) in the Earth's crust and mantle.: Silicates are among our most important rock forming minerals.  They all contain silica and oxygen, but can also contain various metal ions.  Quartz and other forms of pure silica consist only of silica tetrahedron covalently bonded together in a three dimensional framework.  However, in most silicates some of the silica covalent bonds are replaced by ionic bonds to metals, such as aluminum, iron, magnesium, sodium, potassium, and calcium.  These bonds may create planes of weakness and a noticeable cleavage.  You need to become familiar with each of these mineral’s luster, color, hardness, and cleavage to be good at identifying hand samples of these minerals. The following are the most common silicate minerals: 

  Directions:  Look up these minerals in the mineral glossary

  

                                                Luster      Color     Hardness      Cleavage  

  

1.  Olivine                              _____      _____         ____          ___________       

 

2.  Augite (pyroxene)             _____      _____         ____          ___________       

 

3.  Hornblende (amphibole)  _____      _____         ____          ___________       

 

4.  Biotite (mica)                    _____      _____         ____          ___________       

 

5.  Garnet                               _____      _____         ____          ___________

 

6.  Tourmaline                        _____      _____         ____          ___________       

 

7.  Quartz                                 _____      _____         ____          ___________       

 

8.  Orthoclase Feldspar         _____      _____         ____          ___________       

 

9.  Plagioclase Feldspar        _____      _____         ____          ___________       

 

10.  Muscovite (mica)            _____      _____         ____          ___________       

      

 

NOTES:

 

 

 

 

 

 

 

 

 

 

 

IV. FOCUS ON THE MAJOR ROCK-FORMING MINERALS:  Directions: Carefully examine each of the following common minerals. A physical property that is exceptionally helpful in identifying a specific mineral has an “X” . Check only for those properties of each mineral that has an “X”  . 

 

                                            luster     color     hardness     cleavage    streak   acid    magnet    other

 

1.  Quartz                        ____      ____      X____          X_____      ____     ____     ____       ____

 

2.  Plagioclase Feldspar   ____     ____       X____         X_____      ____     ____      ____     ____ 

 

3.  Orthoclase Feldspar    ____      ____     X____         X_____      ____      ____      ____      ____

 

4.  Muscovite (mica)          ____      X____     ____        X_____       ____     ____     ____        ____

 

5.  Biotite (mica)                 ____    X____      ____       X_____      ____       ____      ____      ____

 

6.  Hornblende (amphibole) ____     ____     X____     X _____     ____     ____      ____       ____

 

7.  Augite (pyroxene)         ____     ____      X____      X _____      ____     ____      ____      ____

 

8.  Olivine                          ____      X____     X____      X_____      ____     ____      ____      ____

 

9.  Tourmaline                  ____      X____     X____       X_____      ____     ____      ____      ____

 

10.  Garnet                      ____      ____       X____         X_____      ____      ____      ____      ____

 

11.  Chlorite (mica)         ____      X____       ____       X_____       ____      ____       ____       ____

 

12. Kaolinite (clay)           ____      ____       X ____         _____       ____    X____     ____     X____

 

13.  Magnetite              X____     X ____       ____          _____      X____     ____     X____     ____

 

14.   Hematite                 ____      X____        ____        _____      X____      ____    X____       ____

 

15.   Pyrite                   X ____    X____         ____          _____       X____     ____      ____     ____

 

16.   Chalcopyrite        X ____    X____         ____          _____       X____     ____      ____     ____

 

17.  Galena                  X ____    X____         ____          _____       X____     ____      ____     ____

 

18.   Calcite                   ____       ____        X____        X_____      ____     X____      ____     ____

 

19.   Gypsum                 ____      ____         X____        X_____      ____       ____      ____      ____

 

20.   Halite                     ____      ____         ____        X_____      ____        ____     ____      X____

      

 

 

 

 

 

 

 

X. Unkown Mineral SAmple Identification:

 Directions: Determine the luster, color, hardness, cleavage, streak, and other characterizing physical properties of the following unknown mineral samples. Carefully read the steps listed below:

    1) Note luster as either metallic “M” or nonmetallic “NM”.

    2) Note color as either “Light” , “Dark” or if characteristic, note actual hue, like “green” for olivine. 

    3) Note hardness as either “Hard” (6 and up); “Medium” (between 3 and 6);  or “Soft” (3 down).

    4) Note number of sets of cleavage ( 0 through 4). Also note the angle between two or more sets.

    5) Note the streak color. If you did not need to perform test, then mark with a dash ( ----- ). 

    6) For acid test mark either “Yes” or “No” for doing the acid test.  If you did not need to perform the

       acid test, then mark with a dash ( ----- ). 

    7) Mark either “Yes” or “No” for the magnet test.  If you did not need to perform the magnet test,

       then mark with a dash ( ----- ). 

    6) Finally, using your mineral ID chart, name the mineral that best fits your listed properties.

 

Samp#  luster    color   hardness    cleavage   streak     acid      magnet      Name the Mineral

  

   1.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  2.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  3.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  4.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  5.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  6.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  7.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  8.       _____    ____     ______       _______    _____    ____      ____        _________________

 

  9.       _____    ____     ______       _______    _____    ____      ____        _________________

 

 10.      _____    ____     ______       _______    _____    ____      ____        _________________

 

 11.       _____    ____     ______       _______    _____    ____      ____        _________________

 

 12.      _____    ____     ______       _______    _____    ____      ____        _________________

 

13.       _____    ____     ______       _______    _____    ____      ____        _________________

 

14.       _____    ____     ______       _______    _____    ____      ____        _________________

 

XI. Laboratory Reflection

     Directions: Write a short reflection (about 120 words) about your experience in doing the mineral exercises in lab today.  Include what you learned from this laboratory; what was interesting; the problems and challenges you encountered; and how this lab was designed (the good and/or bad).