Materials Included In Kit

Additional Materials Required

Prelab Preparation

Play a quick game of “Guess Who^©.” This will get the students thinking like detectives and help them understand the process used in identification of an unknown, whether it is an unknown person or an unknown mineral. (Note: “Guess Who” is a mystery face game from Milton Bradley^®, available for under $10.00 from any toy/game store.) Split the class into two teams facing each other and have one student play for each team. During the game, the students will try to guess who the other teams’ mystery person is by collecting evidence from observations made of the suspects. The game provides practice with making observations and gathering evidence—the same processes that will be critical in the mineral-testing lab.

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Follow all laboratory safety procedures. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Excess vinegar may be poured down the drain according to Flinn Suggested Disposal Method #26.

Teacher Tips

• Enough materials are provided in this kit for a class of 30 students working in pairs or for 15 groups of students. One additional large-sized sample of halite (mineral 5) is provided, as this is the mineral suggested for use in the cleavage test (Test 5)—use one halite sample as part of the teacher display set and the other for the cleavage test. Sixteen data tables are provided for your use and convenience. You may make additional 11" x 17" copies of the table. An 8½" x 11" copy of the data table is also provided on page 8 in case you need additional tables and a copier for 11" x 17" is not available. Another option would be to keep one 11" x 17" table blank, and copy it in two halves that can be taped together. More than enough vinegar is available for use in the solubility in a weak acid test. The minerals in this kit can be saved and used to repeat the lab for additional classes. Extra halite and calcite testing chips, sold in packages of 15, are available separately (as these are the minerals that will dissolve—see solubility test results for details).
• This Mineral Detective laboratory activity is designed to engage students in an investigation in which they collect evidence and observations for eight different tests on eight different minerals. At the start of the investigation, each mineral is identified with only a number. At the conclusion of the lab, the students use the evidence gathered to determine the name of each mineral “suspect” by comparing their data with known properties of minerals. A reproducible handout of known properties is provided sd a PDF.
• The minerals for the kit have been carefully chosen so that each sample has one very unique property. The mineral selection process used should assure your students a great deal of success.
• A suggested timeline for this laboratory activity is provided below. The idea is to spread the lab out over a week-long unit on minerals, with some class discussion and some lab time each day. This is the actual timeline used and tested by the author of this lab. Your actual timeline may vary depending on time constraints.
  

  Suggested Timeline: (45–50 minutes per day)

  Day 1—Guess Who^© activator; Introduction to minerals; Test 1 Observations
  Day 2—Test 2 Light Interaction; Test 3 Streak; Test 8 Set up Solubility
  Day 3—Test 4 Hardness; Test 5 Cleavage; Test 6 Smell
  Day 4—Test 7 Ice; Finish observations on Test 8 Solubility
  Day 5—Mineral identification and review

• This kit is based on investigation, data analysis and problem-solving, and is specifically designed to coincide with the NSTA’s national science standards.
• Prior to Testing—Hand out the mineral testing chips and have students place each mineral next to the corresponding number on their evidence/observation table based on the descriptions given. Place the large-sized set of minerals at the front of the room so students can double check if needed.
• Test 1: Observations—If hand lenses are available encourage students to use them. Remind students that a good detective takes precise notes and makes very careful observations.
• Test 2: Light Interaction—This is a good opportunity for students to learn some new vocabulary. Of the three transparent minerals, only the calcite (Iceland spar) displays double refraction. To see this property lay the mineral over a thin line on the paper, and then slowly rotate the mineral.
• Test 3: Streak—Remind the students not to color the streak plates. Only one or two “streaks” are necessary. Students will struggle with the distinction between clear and white streaks. There is not a definite right or wrong answer; have students record whichever they think is appropriate.
• Test 4: Hardness—This is possibly the hardest test (no pun intended) and will require the most time. There is a great deal of logic involved in arriving at a hardness value for each sample. Many minerals vary a bit in hardness, so it is not always possible to get a “right” answer. Students should be as precise as possible. Encourage them to start with finding a range. For example, determine which minerals scratch the nail and which can be scratched by the nail. This will immediately separate the minerals into those with hardness greater than 5 and less than 5. Repeat this logic for all the other tools provided—penny, fingernail, streak plate. (Note: A good discrepant event to capture the students’ interest is to ask them to predict what will happen if a steel nail is “scratched” across the overhead projector. After they have given their dire predictions, rub the nail provided in the kit back and forth on the overhead. The steel nail will not scratch the glass since it has a hardness of 5 and the glass has a hardness of 6.
• Test 5: Cleavage—This test is done as a teacher demonstration to avoid destroying all of the minerals in the kit. The demonstration is dramatic if done on the overhead projector. Carefully tap a nail into one of the large halite teacher samples (mineral 5) provided. After a few firm taps, the mineral will “cleave” along a perfectly flat surface. This sample has perfect cleavage. Tell the students that all of their samples have already been broken from larger pieces, so cleavage of any other samples is not necessary. Students should examine the surface of each mineral and classify the type of cleavage observed.
• Test 6: Smell—This test can be somewhat misleading because sometimes students smell things left on the streak plate from prior tests. Many of the minerals do have strange smells; however, sulfur smells extremely bad—like rotten eggs. This is another test that does not have a “right” answer. Ask the students to record their own observations.
• Test 7: Ice—The rate of melting is controlled by a number of factors. Conductivity, specific heat, and the mass of the sample all affect the rate of melting. The halite will stand out since it begins to dissolve into the ice cube. Ice cubes from standard ice cube trays can be used, or small paper cups can be filled half way with water and frozen. The cups work nicely since they also keep the minerals from falling off.
• Test 8: Solubility—This is a dramatic test because the halite (mineral 5) and calcite (mineral 4) both will dissolve and disappear after a few days in the vinegar. It may be necessary to change the vinegar after a day if some of the calcite remains. Students should also be encouraged to observe the samples carefully. There should be small bubbles coming from the calcite, but not from the halite. When testing solubility in water only the halite will dissolve. This test may take a few days. Materials have been included in the kit to test one set of minerals for the entire class. If the kit will be used year after year, replacement halite and calcite testing chips, as well as additional vinegar, will be needed. See page 14 for ordering information.
• Mineral Identification—After all the evidence has been gathered, hand out the reproducible table of known mineral properties provided on page 11, or have the students use a table provided in their books. Many of the students will have conflicting evidence recorded in their data table. This may actually be good. Students need to learn to deal with real data, and construct their hypotheses based on all the evidence gathered. Students will see that after evaluating all the data against the known properties, each mineral sample has one key characteristic property that should lead to a lot of success at the conclusion of the unit!

Sample Data

Answers to Questions

Going a little further… Ideas, questions and things to do related to each mineral test Many of the questions that follow are intended to be open ended with many possible answers or insights. The answers are only provided as one possible way to look at each problem.

Test 2. Light Interaction Test

1. Which of the minerals might be used for the panes of windows? What other tests should be performed to determine if the mineral(s) could be used for windows?
   Mica in the past was used for windows in ovens. Halite is a clear mineral and could be used but would dissolve in the rain. Calcite is also a clear mineral and would make interesting double refractive windows.

Test 3. Streak Test

2. Some of the minerals had white streaks; some had clear streaks. How could this test be changed to tell the difference between minerals with white streaks and minerals with clear streaks?
   Use a black streak plate instead of a white one.
3. Some minerals are so hard that they won’t crush into a powder when rubbed on a ceramic streak plate (tile). Did any of the minerals seem to scratch the streak plate instead of being crushed? Which? Why did the minerals do this?
   Quartz (Mineral 8) will sometimes scratch the streak plate instead of being crushed. It will do this because quartz and the ceramic streak plates have the same hardness.
4. What common minerals may scratch the ceramic streak plate (tile)?
   Diamonds or any minerals with a hardness greater than 7.

Test 4. Mineral Hardness Test

5. Sometimes pieces of minerals are added to different kinds of soap to make the soap gritty so it can scrub off really tough dirt or scum. The idea is that the gritty mineral will scrub off the scum, without scratching the surface being cleaned. Would it be a good idea to put pieces of quartz into soap used to clean glass? Explain.
   Since quartz has a hardness of 7 and glass has a hardness 6, this would not be a good thing. The soap with the quartz would scratch the glass instead of clean it!
6. Most beaches are made of quartz. When rocks weather, most of the other minerals wear away, but the quartz is left behind. Why is the quartz left behind after all the other minerals are worn away?
   Soft minerals such as mica and calcite get worn away, while harder minerals such as quartz do not get worn away. When many igneous rocks weather, the last remaining mineral is quartz. Therefore, many beaches are made of quartz sand.
7. Many very expensive saw blades are coated with diamonds. Diamond-covered saw blades can cut right through metal, rocks, even concrete! Why are diamonds so good at cutting almost everything?
   Diamonds are good for cutting because they have a hardness of 10 and can scratch and cut almost any material on Earth.

Test 5. Cleavage Test

8. Jewelers sometimes use their knowledge about cleavage to split large gemstones into smaller ones. Which minerals tested in this lab could easily be split into smaller pieces with the same or similar shape as the original mineral?
   Calcite and halite could definitely be cleaved into smaller crystals with similar shapes. (Note: Diamonds are also cut from larger pieces.)

Test 6. Smell Test

9. Have one of your classmates close his/her eyes. Scratch the smelliest mineral on the ceramic plate, then hold it by his nose. Ask him to identify the smell!
   Answers will vary, although the sulfur has a distinctive rotten egg smell.
10. Have you ever smelled anything similar to the smells produced by any of the minerals?
    If something smells similar, it is probably because the chemical compositions are similar. The atoms that make up the mineral are probably the same atoms that make up the object that smells the same! Yes, sulfur is a mineral that smells like rotten eggs.
11. Things that smell a lot usually have very loosely bonded atoms. Which mineral smelled the most? Which mineral was the softest? Which mineral probably has the most loosely bonded atoms?
    Sulfur smells bad and also has a very low hardness. Sulfur most likely has the most loosely bonded atoms.

Test 7. Ice Test

12. Would any of these minerals still melt through the ice if the ice cube had been put in the freezer? Try it!
    This will depend on the temperature of the minerals at the start of the experiment and the temperature of the freezer. This is a great exercise in energy transfer.
13. What will go through an ice cube faster, a big piece of mineral or a small piece? Try the experiment!
    Big minerals hold more heat energy compared to small minerals and should melt the ice faster.
14. Companies mine thousands of tons of one of these minerals each year to melt snow and ice on roads. Which mineral is it? Explain.
    Halite or salt is used in many northern cities to melt ice in the winter. The halite melted the ice very fast in the ice test.
15. Which mineral or minerals would be a good choice to spread on a snowy road to provide traction for a long time?
    Quartz (sand) is often used for traction. Quartz does not melt ice like halite does, but it also does not dissolve and go away. Quartz (sand) also does not contribute to the corrosion of metals like halite (salt) does.

Test 8. Solubility Test

16. Some buildings and statues are made with limestone. Limestone has a lot of mineral 4 in it. Would you like to live in a house made of limestone if the house was in an area that received a lot of acid rain?
    Many buildings and statues made of limestone are being devastated by acid rain. The solubility test showed that mineral 4 is soluble in acid. Granite is a much better building material.
17. Acid rain poisons some lakes. Lakes can often be treated by adding limestone, which contains a lot of mineral 4 in it. Limestone can neutralize the acid in the lakes. Would water, with limestone dissolved in it, have a pH above or below 7? Why?
    Water with limestone dissolved in it has a pH above 7. This could be inferred because mineral #4 reacted with the acid to produce carbon dioxide gas.
18. Which dissolves better in water, sugar or salt? Obtain two beakers of the same size. Fill each 1⁄2 full of water. Start adding level spoonfuls of sugar to one beaker, and level spoonfuls of salt to the second beaker. After adding the sugar or salt, stir the water until all of the solid is dissolved.
    Sugar has a much greater solubility in water when compared to salt. The difference is even greater when hot water is used.
19. Will sugar and salt dissolve in oil? Pour some vegetable oil into a cup. Try dissolving sugar in the vegetable oil. Repeat this test for salt. Does it work as well as the water?
    Salt will not dissolve at all in oil. Sugar will not dissolve well in oil. Both sugar and salt are much more soluble in water.
20. Minerals that dissolve in water have bonds between their atoms that can be pulled apart by the water molecules. Based on the water dissolving test, which minerals are held together by bonds that can be pulled apart by water molecules?
    Halite dissolves easily in water. It is a very polar molecule and dissolves easily in water which is a very polar solvent.

Teacher Handouts

11913_Teacher1.pdf

References

Special thanks to Bill Grosser, Glenbard South H.S., Glen Ellyn, IL, for providing Flinn Scientific with this laboratory activity.

Introduction

Minerals—how can scientists tell which is which? Scientists gather evidence by performing laboratory tests. In this lab, tests will be performed on eight different unknown mineral specimens. The results of these tests will be used to identify each by name.

Concepts

• Mineral testing
• Mineral identification

Background

What is a Mineral? Many of the rocks that make up the Earth’s crust consist of different combinations of minerals. Minerals are the building blocks of rocks. To be considered a mineral the following five criteria must be met. A mineral must:

• Be a solid.
• Occur naturally.
• Be inorganic (Never alive!).
• Have a definite chemical composition.
• Have its atoms arranged in an orderly pattern.

There are over 250 different minerals on Earth! Each mineral has a distinct chemical composition, which gives each mineral unique properties. Geologists identify minerals much the same way detectives solve crimes. The first step is to gather as much evidence as possible. After all the evidence is collected, a hypothesis is made. Detectives use evidence to decide who is guilty. In this laboratory activity, the evidence will be used to identify eight different minerals by name. During the entire activity, all evidence will be recorded in the “Observations and Evidence” table. At the beginning of the lab each mineral will only be identified with a number. At the end of the lab, all the evidence gathered will be compared to known properties of minerals. By comparing the evidence gathered against the known properties, each mineral should be able to be correctly named. Good luck!

Materials

Safety Precautions

Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Follow all laboratory safety procedures.Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Test 1. Observations

The first thing any good detective does when arriving at a crime scene is to make careful observations.

1. Obtain eight different mineral samples to be tested and identified. The mineral samples will initially be identified using numbers 1–8. Note: By the end of this laboratory, the minerals will be identified by name.
2. Lay the Observations and Evidence table on the tabletop and set each mineral sample next to its corresponding number on the data table. A very brief description of each mineral is provided in the table below so that the mineral may be matched with its number.
   {11913_Procedure_Table_1_The Mineral Suspects}
3. Use a magnifying glass to carefully observe each mineral. Record a detailed description of each sample in the Observations and Evidence table. Be sure to include physical properties (e.g., color, shape, distinguishing features, unique characteristics). Note: Descriptions should be clear enough that if the eight samples were moved or mixed up, they could be easily identified by number on the data table.

Test 2. Light Interaction Test

The way that light bounces off or passes through a mineral tells something about how the atoms inside the mineral are arranged. The atoms in some minerals let light rays pass through, while some minerals have arrangements that make the light bounce right off. Each condition has been given a different name.

4. Look carefully at each mineral and decide if each is opaque, translucent or transparent.

   Use the following definitions to classify each mineral:

   Opaque: No light can pass through the mineral. When the mineral is held up to a light, no light shows through.
   
   Translucent:Some light can pass through, but you can’t see through the mineral. A mineral is translucent if the edges look lighter when it is held up to a light.
   
   Transparent: Light rays can pass right through the mineral. Transparent minerals look like glass—you can see right through them.

5. Record all observations in the Observations and Evidence table.
6. Some transparent minerals also show a unique property called double refraction. Double refraction is caused when the light rays are bent—making everything you look at through the mineral appear double!
7. Test each transparent mineral for double refraction. To do this, lay each transparent mineral across the straight and wavy lines below or over some writing. Look at the lines through the mineral. Slowly rotate the mineral and see if any of the lines appear double, causing “double vision” to occur.
8. Record all observations in the Observations and Evidence table.

Test 3. Streak Test

The “streak” of a mineral is the color of the mineral’s powder. The streak of a mineral can be different than the color of the mineral itself. Sometimes the color of the outside of a mineral is changed by contact with the air, rain or water and other minerals in the ground.

9. Obtain a white streak plate.
10. Take each mineral sample and rub it once or twice on the streak plate.
11. Record the color of the powder that rubs off each mineral in the Observations and Evidence table.

Test 4. Mineral Hardness Test

Hardness describes how resistant a mineral is to being scratched. This is different than breaking or shattering a mineral. To determine hardness, either scratch the mineral or, use the mineral to scratch something else. A geologist named Friedrich Mohs developed a scale for rating the hardness of minerals. The higher the number, the harder the mineral, with 10 being the hardest. Each mineral will scratch those with a lower number, but will not scratch those with a higher number.

Determine the hardness of each mineral by trying to scratch each one with your fingernail, the penny, the nail or the streak plate.

12. Obtain a steel nail. Determine the hardness of each mineral by first trying to scratch each with a steel nail (hardness = 5). This is easiest to do on a flat surface of a mineral.
13. Split the eight minerals into two groups—minerals that the steel nail can scratch (hardness less than 5) and minerals that the nail cannot scratch (hardness greater than 5). (Note: Minerals that the steel nail can’t scratch should be able to scratch the steel nail!)
14. For each mineral that was classified with a hardness of less than 5, try to scratch each with a copper penny (hardness = 3) and then with your fingernail (hardness = 2). Categorize each mineral using the same logic as in step 13.
15. For each mineral that was classified with a hardness of greater than 5, try to scratch each with a ceramic streak plate (hardness = 7). Categorize each mineral using the same logic as in step 13.
16. Estimate the hardness of each mineral based on the hardness of each comparison tool. Record the hardness of each mineral in the Observations and Evidence table.

Test 5. Cleavage Test

Cleavage is a word used to describe how a mineral splits or breaks. Some minerals form perfectly flat surfaces when they break. This is called cleaving. Mineral 3 is an example of a mineral that has perfect cleavage. Thin sheets of the mineral can actually be peeled off, and the surface left behind is perfectly flat! Most minerals cannot be easily peeled apart like mineral 3. To test most minerals for cleavage they need to be hit or shattered.

The teacher will demonstrate how minerals are tested for cleavage by breaking mineral 5.

Safety Precaution: Testing for cleavage requires shattering the mineral with a hammer. Safety goggles should be worn while doing this test!

17. All of the minerals being tested have already been broken from larger pieces. Look at the broken surfaces on each mineral sample and describe the mineral’s cleavage. Use the following definitions to describe each mineral.
    
    

    Use the following definitions to describe each mineral:

    Perfect Cleavage: The broken surface is perfectly flat. Light reflects off when tilted back and forth.
    
    Good Cleavage: Some of the broken surfaces appear perfectly flat. When the mineral is tilted back and forth in the light, there appears to be one position that reflects light very well.
    
    Poor/No Cleavage: The broken surfaces are irregular. Although the mineral might be shiny, none of the surfaces are perfectly flat.

18. Record all descriptions in the Observations and Evidence table.

Test 6. Smell Test

Some minerals have very unique or distinctive smells. It is easiest to smell a mineral if you have a fresh sample of its powder.

19. Test the minerals in the following order: 8, 7, 6, 5, 4, 3, 2, 1. Rub each mineral back and forth a few times on the streak plate. Immediately smell the powder.
20. Record all observations in the Observations and Evidence table.

Test 7. Ice Test

Some minerals behave very uniquely when they come in contact with ice. In this test, each mineral is placed on an ice cube to see what happens!

21. Put nine ice cubes onto a piece of paper towel. Put one piece of each mineral onto each ice cube. (Note: One ice cube will be empty to serve as a “control.”)
22. Watch the ice cubes for five minutes. Record all observations in the Observations and Evidence table.

Test 8. Solubility Test
Solubility is a word used to describe how well things dissolve. In this test, the solubility of the minerals will be tested in two liquids, water and vinegar (acetic acid). The solubility test will be performed as a class experiment.

23. Fill eight 100-mL beakers with about 50 mL of tap water.
24. Fill eight other 100-mL beakers with about 50 mL of vinegar, a weak acid.
25. Place one piece of each of the minerals in each beaker of water and in each beaker of acid. Label the beakers. Allow the minerals to sit in the liquids for one or two days or until no further observable changes are apparent. Use the following terms to describe each mineral:
    
    

    Use the following terms to describe each mineral:

    Soluble: The mineral dissolves easily in the solvent, either water or acid.
    
    Slightly soluble: The mineral appears to dissolve to some extent in the solvent.
    
    Insoluble: The mineral does not appear to dissolve at all in the solvent.

26. Record all observations in the Observations and Evidence table.

Mineral Identification

27. Identify each mineral by name in Column 1 of the Observations and Evidence table. Use a table of known mineral properties (either from your textbook or provided by your teacher). Some recorded evidence may be conflicting—this is okay. Evaluate all the data against the known properties and make your best guess.

Student Worksheet PDF

11913_Student1.pdf