Minerals Lab 2
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School
Colorado State University, Fort Collins *
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Course
121
Subject
Geology
Date
Apr 3, 2024
Type
Pages
4
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GEOL 121 –
S24 Name_____________________________- Lab Section__________________ 1 MINERALS LAB 2
Learning Objectives At the end of this lab students will be able to: ●
Use physical properties to identify minerals. ●
Develop and produce a system for identifying different minerals via a dichotomous key flow chart. Step 1: Identify the suspects The set of minerals from Minerals Lab 1 have been identified in the table below. Check your observations of the mineral properties with those listed in the table. Revisit any observations that differ from the ones listed. Discuss with your group and your TA why you think your observations differ from the listed properties. A. Plagioclase Feldspar NaAlSi
3
O
8
to CaAl
2
Si
2
O
8
in varying proportions
Color: white to green-gray Streak: white/colorless Luster: nonmetallic (milky to translucent) Hardness: 6 Cleavage: good, 2 planes at 90º Striations
on cleavage planes Specific Gravity: 2.62
–
2.75
B. Muscovite KAl
2
(AlSi
3
O
10
)(F,OH)
2
Color: colorless to pale yellow/gold Streak: white/colorless Luster: nonmetallic (glassy, milky) Hardness: 2
–
2.5 Specific Gravity: 2.8
–
2.9 Cleavage: perfect in 1 direction C. Halite NaCl Color: colorless Streak: white/colorless Luster: nonmetallic (glassy) Hardness: 2.5 Cleavage: perfect, 3 planes @ 90º Specific Gravity: 2.1-2.6 Salty taste
D. Magnetite Fe
3
O
4
Color: dark gray to black Streak: black Luster: metallic Hardness: 5.5-6.5 Specific Gravity: 5.2 Cleavage: none Magnetic
E. Pyrite FeS
2
Color: brassy yellow Streak: green-black to black Luster: metallic
Hardness: 6
–
6.5 Specific Gravity: 5.02 Cleavage: none, concoidal fracture
F. Quartz SiO
2
Color: colorless, white, pink, any color Streak: white/colorless Luster: nonmetallic (glassy) Hardness: 7 Cleavage: None Conchoidal fracture
common Specific Gravity: 2.65
Minerals Lab 2 GEOL 121
2 G. Calcite CaCO
3
Color: colorless, white, yellow Streak: white/colorless Luster: nonmetallic (glassy) Hardness: 3 Specific Gravity: 2.71 Cleavage: perfect, 3 planes @ 75º Effervesces in dilute HCl acid H. Amphibole Ca
2
(Mg,Fe(Ca,Na)
2-
3
(Mg,Fe
+2
,Fe
+3
,Al)
5
Si
6
(Si,Al)
2
O
22
(OH)
2
Color: black, dark green, dark brown, dark gray Streak: white/colorless Luster: nonmetallic (vitreous to dull) Hardness: 6 Cleavage: Imperfect 2 directions at 56° and 124° / uneven Specific Gravity: 3
–
3.4 I. Galena PbS
Color: gray Streak: gray Luster: metallic Hardness: 2.5 Cleavage: good, 3 planes @ 90º Specific Gravity: 7.5 (very dense) Sulfur smell on fresh surfaces J. Biotite K(Mg,Fe)
3
AlSi
3
O
10
(OH)
2
Color: brown to black Streak: white to gray Luster: nonmetallic (pearly to submetallic) Hardness: 2.5-3 Specific Gravity: 2.7-3.4 Cleavage: Single perfect cleavage to produce thin flexible sheets or flakes.
K. Potassium Feldspar KAlSi
3
O
8 Color: typically shades of peach, orange, or red Streak: white Luster: nonmetallic (vitreous (glass-like) to porcelaneous (porcelain-like)) Hardness: 6 Specific Gravity: 2.6 Cleavage: One perfect cleavage and one good cleavage, meet at nearly 90
L. Pyroxene (NaCa)(Mg,Fe,Al)(Al,Si)
2
O
6 Color: Usually dark green, dark brown or black Streak: white, greenish white or gray Luster: nonmetallic (vitreous (glass-like)) Hardness: 5-6 Specific Gravity: 3.2-3.5 Cleavage: Two directions, that meet at nearly right angles (87
and 93
) Step 2: Build your key
In Minerals Lab 1, you became familiar with mineral properties and how to evaluate and test them: color, luster, streak, hardness, cleavage, density, reaction to acid, and magnetism. Not only do the physical properties of minerals determine what people use them for, but geologists also use these same physical properties to identify minerals too! Next, you will be constructing a flowchart that will enable you (and others!) to identify the 12 minerals that you have examined so far. Construct a Flow Chart for Mineral Identification Flowcharts are simple diagrams that show step-by-step instructions for completing a task or solving a problem. A few examples of flow charts are shown below.
Minerals Lab 2 GEOL 121
3 Your flow charts will be set up as a dichotomous key. A dichotomous key is a scientific tool used to identify different objects or organisms. In geology, it is particularly useful for identifying minerals, rocks, or fossils. The word "dichotomous" means divided into two parts. Therefore, a dichotomous key always presents two choices in each step, leading to the identification of the specimen or object. How to Create a Dichotomous Key:
1. Gather Specimens
: Begin by collecting the set of specimens that you want to identify using the key. 2. Research and Observation
: Study the specimens. Note down their distinct characteristics such as color, hardness, luster, crystal form, etc. (You have already done this.) 3. Categorize Characteristics
: Arrange these characteristics from most general to most specific. This arrangement helps in starting with broad distinctions and narrowing down to more specific ones. 4. Create Binary Choices
: For each step, devise two contrasting statements (e.g., "has a metallic luster" vs. "does not have a metallic luster"). Each choice should lead to another set of choices or to the identification of the specimen. 5. Test and Refine
: Use the key to identify unknown specimens. Make adjustments if you find any step unclear or misleading. Your group’s task is to construct a flowchart that shows how to identify each of the minerals. A large sheet of blank paper has been provided by your TA
. How your group’s chart looks will be up to you, but each line should end at a box with the name of one of the 12 minerals. Here is a hint to get you started: Can you divide the 12 minerals into two groups based on their similarities in some physical property? If so, start there. Then within each group, try to divide based on another property...and so forth, so that by following each line/set of arrows to the end, you can arrive at a determination of the name of the mineral. This will take some trial and error. Here is an example flowchart for the identification of plant types:
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Minerals Lab 2 GEOL 121
4 You should work together as a group, but each student should create their own flow chart. You will be able to use your flow chart on the Minerals Quiz. Step 3: Solve the case! Once you have completed your flow chart, turn in your set of samples to your TA and get three new unknown samples. These samples will be one of the 12 minerals that you have included in your flow chart. Use your flow chart to identify the three minerals. Write your identifications and explain your reasoning on the Demonstration of Understanding page that your TA will give you.