Minerals. Mohs Scale of Hardness

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1 Part I: Testing Mineral Properties You will perform the following tests on each mystery mineral as directed by your teacher. Be sure to record your observations in the appropriate row of the data table. Hardness Test Generally speaking, all minerals are hard. But did you know some minerals are harder than others? When you test for hardness you are measuring how resistant a mineral is to being scratched. Mohs Scale of Hardness is used to determine the hardness of materials. Mohs Scale identifies a mineral s hardness starting with 1 (easily scratched) and continues to 10 (cannot be scratched). By comparing the hardness of the mystery mineral to that of a substance with a known hardness, you are able to roughly identify the hardness of the mineral using a number from 1 to 10. When you know the hardness of a mineral, you are one step closer in identifying it. Mohs Scale of Hardness 1. Talc 2. Gypsum 3. Calcite 4. Fluorite 5. Apatite 6. Orthoclase 7. Quartz 8. Topaz 9. Corundum 10. Diamond In this activity, you will use more common substances to test for hardness instead of the minerals of Mohs Scale of Hardness. Follow the procedure below, record your observations on the data chart and complete the Hardness Test questions in your Student Journal. Be sure to record your data for the correct station. Pick up a mystery rock and complete the following steps: 1. Try to scratch the surface of the mineral with your fingernail. If you can very easily scratch the surface of the mineral, its hardness is 1. If not, go to the next step. 2. If you can scratch the surface of the mineral with some effort, then the hardness is 2. If not, go to the next step. Continue to the next page. 1

2 Hardness Test, continued 3. Try to scratch the mineral with the penny. If the penny scratches the surface of the mineral, then the hardness is 3. If the penny does scratch the surface of the mineral, go to the next step. 4. Try to scratch the mineral with a nail. If the nail very easily scratches the mineral, then the hardness is 4. If not, go to the next step 5. If the nail scratched the mineral with some effort, then the hardness is a 5. If not, then go to the next step. 6. If the mineral can be scratched by a steel file but barely scratches glass then the hardness is a 6. If not, then go to the next step. 7. If the mineral easily scratches glass but cannot scratch a steel file then the hardness is a 7. If it easily scratches the steel file, then the hardness is 8 or greater. 8. Always retest your scratches to make sure the hardness is as accurate as possible. 9. Record the hardness of the Mystery Mineral on the data table in Part I of your Student Journal. 10.Follow the above steps for the other mystery minerals and record your findings. Remember to record your results on the data table, and then answer the questions for Station I in your Student Journal. Description Easily scratched by a fingernail Scratched by a fingernail Is scratched by a penny Easily scratched by a nail Difficult to scratch with a nail Scratched by a steel file Easily scratches glass Scratches a steel file Hardness or greater By identifying the streak of a mineral, you are one step closer to identifying it. Answer the questions for Hardness Test and record your data in the chart in the Student Journal. 2

3 Color, Transparency, and Crystal Shape 1.Pick up each mineral and observe how it looks using the information below about mineral color, transparency, and crystal shape. Use the hand lens to help you observe. 2.When testing for transparency, hold the Petri dish with the sample up to the classroom overhead lights so that the sample is between you and the lights. If some light shines through it the mineral is translucent. If you can see through the mineral, it is transparent. If no light shines through, the mineral is opaque. Color: The mineral s color helps identify it, but is not always reliable. A mineral s surface color can be misleading because some minerals have a color range depending on slight variations in the elements and compounds that are present. Transparency: Can you see through the mineral? If you can see through the mineral then it is transparent. If the mineral allows only some light to pass through, it is translucent. If you can t see through the mineral, then it is opaque Transparent Translucent Opaque Continue to the next page. 3

4 Color, Transparency, and Crystal Shape, continued Crystal Shape: All minerals have a crystalline shape, although most of the time they can only be seen under extremely high magnification, if at all. Two of your unknown mineral samples, pyrite and quartz, may show visible crystalline shape. Use the images below to watch for these shapes in your unknown samples. Classify the crystal shape in your data table as hexagonal, cubic, or unknown. Hexagonal Cubic 3.Record your observations about color, transparency, crystal shape, and texture in the correct row of the data chart. Remember to answer the questions for Color, Transparency and Crystal Shape in your Student Journal when you are finished. Answer the questions for Station 2 and record your data in the chart in your Student Journal. 4

5 Luster Test Luster can be generally classified as metallic (shiny) or non-metallic (dull). If you have a mineral that has a non-metallic luster, you can further describe it with the words such as earthy, resinous, waxy, glassy, and pearly. Metallic: light is reflected by the mineral, shiny, has the look of metal Non-Metallic (duller) Earthy: light is absorbed by the mineral, has the look of dried mud Non-Metallic (duller) Resinous: light is somewhat absorbed by the mineral, has the look of resin or dried glue Non-Metallic (duller) Waxy: light is somewhat absorbed by the mineral, has the look of wax Non-Metallic (duller) Glassy: light is mainly reflected, has the look of a glass surface Non-Metallic (duller) Pearly: light is somewhat absorbed by the mineral, has the look of pearl 1. Pick up each mineral and position it under a light source. Observe how the light reflects off the mineral. Luster describes how light reflects off the mineral. 2. Record your observations about luster for each of your mystery minerals on the data chart in the correct row. Remember to answer the questions for Luster in your Student Journal when you are finished. By determining the luster of a mineral, you are one step closer to identifying it. Answer the questions for Luster and record your data in the chart in your Student Journal. 5

6 Streak Test Streak is the powder color a mineral shows when it is rubbed on a piece of unglazed porcelain. The unglazed porcelain is known as a streak plate. Streak plates look like a piece of tile. The streak of a mineral is more reliable than the color of a mineral. Streak color of a mineral s powder does not change even if there are minor impurities that cause changes to the surface color of the mineral. 1.Ensure the surface of your streak plate is clean. 2.Take one of the minerals and rub the mineral against the streak plate. Notice the color of the powder left by the mineral on the streak plate. By identifying the mineral s streak, you are one step closer to identifying it. 3.Record the color of the powder on the streak plate for each mineral. Make sure the streak plate is cleaned after each streaking. 4.Record your observations about the mineral streaks on the data table and answer the Streak questions in the Student Journal. Answer the questions for Streak and record your data in the chart in the Student Journal. 6

7 Density Test Determine the density of each of the mystery minerals. Recall that density compares the mass to the volume of an object. So, to calculate density you must know the mass, or amount of matter in an object, and the volume, or the space the object takes up. Once you determine the mass and volume of the object you can use the formula for density. Density = Mass/Volume Knowing the density of a mineral sample is very useful, because the density of minerals is very consistent, meaning it does not change very much from one sample to the next. Every piece of pure gold has a density very close to 19.3 g/cm³. The mineral pyrite, also called fool s gold, looks similar to gold, but every piece of pyrite has a density around 5.1 g/cm³. So density is a good test for determining if a mineral sample is real gold or fool s gold. The table to the right lists mass and volume data for example samples of each mystery mineral. Use the mass and volume data to determine the density (to the nearest tenth) for each mystery mineral. Record the density on your data table and answer the questions in Station V section in your Student Journal. Mass and Volume of Mystery Mass Volume Mineral A 10.8 g 4 cm³ Mineral B 8.4 g 4 cm³ Mineral C 10.8g 4 cm³ Mineral D 12.8 g 4 cm³ Mineral E 12.4 g 4 cm³ Mineral F 21.2 g 4 cm³ Mineral G 20 g 4 cm³ Mineral H 10.4g 4 cm³ Answer the questions for Density and record your data in the chart in the Student Journal. 7

8 Part II: Identify the Mystery You have collected a lot of information to help determine the identity of the minerals. Compare the data that you collected and recorded on your data table to the mineral KEY below. Do your best to determine the identity of all of the materials and record the name of each mineral on Part II of your Student Journal. Finally, complete the Reflections and Conclusions questions. Approx Hardness Color/ Transparency Calcite 3 Variable, usually white or colorless, transparent or translucent Fluorite 4 Variable, green, pink, yellow, purple, blue, colorless, transparent Hematite 6 Reddish gray to black to blackish red, opaque Limonite Brown or yellowish brown, opaque Pyrite 6 Brassy yellow, greenish yellow, opaque Crystal Shape Unknown Unknown Luster Non-metallic Glassy Non-metallic Glassy Streak White Unknown Metallic Reddish Brown Unknown Non-Metallic Brownish Earthy yellow to yellow Cubic Metallic Greenish black Approximate Density 2.7 g/cm³ White g/cm³ 5.3 g/cm³ g/cm³ 5.0 g/cm³ Quartz 7 Variable, clear, white, purple, pink, gray, transparent to translucent Sulfur 2 Yellow, transparent to opaque Hexagonal Non-Metallic Glassy Unknown Non-Metallic Resinous White Yellowish white 2.6 g/cm³ 2.1 g/cm³ Talc 1 Green, gray, white, silvery, Transparent to translucent Unknown Non-Metallic Resinous, Pearly or Waxy White g/cm³ Continue to the next page. 8

9 Technology Connection for Part II 1.Input your data in a spreadsheet program. 2.Sort the data by hardness to create a list of softest to hardest minerals. 3.Sort the data by density to create a list of most dense to least dense minerals. 4.Use the sorted data to identify the mystery minerals. Complete Part II and the Reflections and Conclusions questions in your Student Journal. 9