NAME DATE PARTNERS EXPLORING EARTH MATERIALS Every time we pick up a solid non-organic (inorganic) earth object we have a tendency to call it a rock or a stone. Did you know that geologists have a special property in mind when they call something a rock? Terminology is important in science and words that are synonyms in everyday language may convey different meanings in a specific science discipline. Here's a chance to do some observing and classifying to see if you can come up with characteristics that geologists use to distinguish inorganic materials, specifically rocks and minerals. You open a drawer in your classroom and find a collection of inorganic materials that you call rocks. A friend who has some geology knowledge says that you really have a mixed collection of rocks and minerals but she won t tell you which is which until you do make some observations. She promises to give you the specific names of each object in the drawer if you can find the characteristic(s) that are the basis for classification as a rock or mineral. What would you look for? Let s Explore! Activity 1: Is it a Rock or a Mineral? 1. Observe the collection of materials on the lab bench. As a group, decide on characteristics you will use to separate the materials into groups. Your characteristics may be color, shape, sizes, for example. Briefly describe your characteristics. Keep in mind that when you describe the characteristics any other person should be able to use them and place the same objects in the same groups as you do. Sort the objects based on your characteristics. Fill in the table below giving a brief description of the materials in each group. You may have more or fewer groups than shown in the table below. Explorations in Earth and Space Science PSC 121 Prince George s Community College 3
Group Group Group Group Group Characteristics Objects in Group (brief description) 2. Now switch to another set of samples from a group near you and see if your characteristics apply for the new set. Group Properties Objects in Group (brief description) Group Group Group Group Did your characteristics work to classify the new set? Explain. 4 Explorations in Earth and Space Science PSC 121 Prince George s Community College
3. Now, decide on a single characteristic that will divide the samples into only two groups (if you had more than two before). Re-sort your samples based on this property. Group Group Group Properties Objects in Group (brief description) Activity 2: What Mineral Is This? Now you should have some understanding of how geologists distinguish between rocks and minerals. As you have discovered, a mineral is made up of only one compound, one specific set of atoms. A rock is generally made of many different minerals. Let s take a look at minerals and investigate the properties used to identify them. At each lab bench there should be the following equipment: a white plastic mineral tray, glass plate, streak plate (white, ceramic square), file, penny, magnet, and small bottle of acid. On the next page you will find a grid that resembles the tray. Fill each section of the tray with the mineral specified. The minerals are located in labeled drawers of two small cabinets available in the lab. Use this grid sheet as an identification guide as you investigate the mineral properties. THERE IS A TABLE TO RECORD MINERAL PROPERTIES NEAR THE END OF THIS ACTIVITY. Explorations in Earth and Space Science PSC 121 Prince George s Community College 5
Mineral Grid Use this sheet to obtain and keep track of the minerals you use in Activity 2. This grid should resemble the plastic tray you have in the lab. Calcite (Icelandic Spar) Gypsum Graphite Corundum Fluorite Quartz (Amethyst) Quartz (Rose Quartz) Pyrite Talc Hematite Galena Sulfur Kaolinite Calcite (Chalk) Muscovite Magnetite 1. Observe (feel free to handle) several of the minerals that are available. What characteristics do you notice that might assist you in identifying a sample? Would you be willing to rely on only one characteristic to identify a mineral? Explain. Mineral Properties Geologists use certain properties to identify minerals. Hardness, as the name implies, is a measure of how hard a mineral is. Geologists use the Mohs Scale of Hardness. On this scale, objects with a higher number will scratch anything with a lower number. Below is a table with some hardnesses on the Mohs scale for reference minerals and common objects. 6 Explorations in Earth and Space Science PSC 121 Prince George s Community College
Hardness Reference Mineral Common Objects with This Hardness 10 diamond 9 corundum 8 topaz 7 quartz 6.7 File 6 orthoclase 5.5 glass, steel knife 5 apatite 4 fluorite 3.5 copper penny 3 calcite 2.5 Fingernail 2 gypsum 1 talc Minerals have different colors when you look at them and this can be used for identification for some but not all minerals. Many minerals also show a certain color when powdered or when they are rubbed on a piece of baked white clay. This powdered color of a mineral is called its streak. The streak color may be the same or different than the mineral color. Some minerals appear in more than one form with different colors. However, the streak is the same no matter what overall color the mineral has. Some minerals contain carbonates. These minerals "fizz" when you put a drop of acid on them. This acid test is a very good indicator of carbonate minerals. Occasionally the acid test will produce an odor similar to rotten eggs. This occurs when you have a sulfide-containing mineral. Minerals can also be identified by their luster. Luster is how they appear in light. Some types of luster are glassy, metallic, silky, and dull. Some minerals feel much heavier or lighter than you might have expected for their size. This property is called density or specific gravity. This can be a quick indication of a mineral's composition. Sometimes a geologist can figure out what a mineral is using only one test but it takes a lot of experience. The more tests you do on a mineral, the better your chances of identifying it. Now Let's Investigate Your Minerals! 2. Slide a piece of quartz across the glass plate with some effort. What does quartz do to a glass plate? What does this tell you about one property of quartz? What does your fingernail do to calcite? What information does this convey? Explorations in Earth and Space Science PSC 121 Prince George s Community College 7
What does your fingernail do to gypsum? Why? 3. Look at the two purple samples on the instructor s table. Try measuring some of the properties other than color. What do you find? Are these samples the same mineral? Explain. _ Does the color of a mineral always work as a property to identify minerals? Explain based on the previous samples samples. 4. Now try as many tests (hardness, streak, acid ) as you can on each of your minerals and record your observations in the table for known minerals at the end of this activity. 5. Now that you are finished your observations, answer the following questions. a. Which properties are best for identification? Why? b. Is the same property good for identifying all minerals? Explain. c. Can you identify a mineral with only one property? Why or why not? 8 Explorations in Earth and Space Science PSC 121 Prince George s Community College
5. Now it's time to try and identify some unknown minerals based on your experience. Perform the same tests you did before on the numbered unknown samples. Based on your observations, determine the identity of each unknown mineral. The unknown minerals are ones that you tested in the first part. Record your observations in the data table below. UNKNOWN MINERALS Mineral Number 1 Hardness Color Streak Luster Density Acid Test 2 3 Unknown Mineral # 1 is because Unknown Mineral # 2 is because Unknown Mineral # 3 is because 6. Be sure to rinse with water, dry, and return the minerals to the appropriate drawer when you are finished. Explorations in Earth and Space Science PSC 121 Prince George s Community College 9
KNOWN MINERALS Mineral Color Hardness Streak Luster Density (low, medium, high) Calcite (spar) Acid Test Gypsum Graphite Corundum Fluorite Amethyst Rose Quartz Pyrite Talc Hematite Galena Sulfur Kaolinite Calcite (chalk) Muscovite Magnetite 10 Explorations in Earth and Space Science PSC 121 Prince George s Community College
Activity 3: Igneous, Metamorphic, or Sedimentary? You know that minerals have distinctive characteristics but are all rocks the same? What characteristics or processes do you think might differentiate rocks from each other? 1. Locate the groups of rocks provided by the instructor. They will be labeled igneous, sedimentary, and metamorphic. Examine one set at a time. Record the characteristics common to each sample in the set. Record any unique features. Continue with the other sets. Igneous Rock Type Common Characteristics Uncommon Features Sedimentary Metamorphic Explorations in Earth and Space Science, PSC 121, PGCC
a. What characteristics could indicate to you that a rock is igneous? b. What properties are identifiers of sedimentary rocks? Is there any evidence in the rocks about how they were formed? c. What would you look for to classify a rock as metamorphic? STOP HERE FOR DISCUSSION 2. Now look at the group of numbered, unidentified rocks. Based on the characteristics you outlined, determine whether each rock is igneous, sedimentary, or metamorphic. Be sure to include you reason(s) for the decision. Rock Number Type of Rock Justification for Type 1 2 3 4 Did you have any you are unsure of? Why? 12 Explorations in Earth and Space Science PSC 121 Prince George s Community College