Introduction to Geological Sciences

Mineral Properties

Others taught me with having knelt at well-curbs
Always wrong to the light, so never seeing
Deeper down in the well than where the water
Gives me back in a shining surface picture
Me myself in the summer heaven godlike
Looking out of a wreath of fern and cloud puffs.
Once, when trying with chin against a well-curb,
I discerned, as I thought, beyond the picture,
Through the picture, a something white, uncertain,
Something more of the depths--and then I lost it.
Water came to rebuke the too clear water.
One drop fell from a fern, and lo, a ripple
Shook whatever it was lay there at bottom,
Blurred it, blotted it out. What was that whiteness?

Truth? A pebble of quartz? For once, then, something.

Robert Frost, from “A Line –Storm Song

Introduction: At each station, there is an activity for you to do to investigate properties of minerals. Each team can move around the room at their own pace answering questions below for each station. Complete the stations in any order. Refer to your lab book (Chapter 1) for background information as needed. Ask me questions if you need help. Complete written answers on a separate sheet of paper.

Outcomes: Students will:

• Use various reference materials together with critical thinking and evaluative skills to identify minerals
• Learn the importance of using mineral properties to actively examine minerals in order to develop concrete conclusions
• Work collaboratively to make observations and develop conclusions

STATION 1: The property of luster.

Materials at this station: Samples of quartz, biotite, hematite, feldspar, amphibole (hornblende), galena, graphite, and pyrite.

Question 1: Review the information about luster in your lab manual (p. 5). Determine the luster of each mineral as metallic or non-metallic, and write them under each heading below.

Metallic luster Non-metallic luster

Question 2: Examine the information in Table 1.2 in your lab manual. Does your description of luster match that given in the manual? Review your answers and make corrections to be sure that you understand the differences between metallic and non-metallic luster.

Question 3: Look at the chemical formulas of the minerals with metallic luster in Table 1.2: do they generally contain metals such as copper (Cu), iron (Fe), lead (Pb), and zinc (Zn)? Write down some of the formulas. Which minerals is an exception?

Question 4: Silicate (containing Si & O) minerals that have metals, such as iron (Fe), do not have a metallic luster. Which of the minerals you looked at fall into this category?

STATION 2: Color and streak of minerals

Materials at this station: Samples of quartz, fluorite, amphibole (hornblende), hematite, garnet, and sphalerite. Streak plates.

Question 5: Color is probably the most obvious property. Some minerals have one characteristic color or a narrow range of colors, while other minerals can have many colors. Examine the minerals in the trays. Which of these minerals show variability in color (i.e., different colors in different pieces or places)?

Question 6: Streak is the color of a mineral when powdered (p.9). Take each sample and CAREFULLY scrape it across the streak plate, keeping the plate flat on the table. Blow off the loose powder and examine the color of the mineral streak on the plate. Write the streak of each mineral in the blanks below.

_____________________Fluorite __________________ Hematite ______________ Quartz

_________________ Sphalerite ______________ Amphibole _________________ Garnet

Question 7: Which minerals have a streak different from their color?

STATION 3: A mineral with a magnetic personality

Materials at this station: 1. Samples of pyrite, hematite, galena, magnetite, and hornblende. 2. A magnet.

Question 8: There is only one common mineral in the world that is always strongly magnetic. Use the magnet at this station to find out which mineral this is.

Question 9: You should not be surprised that iron (Fe) is a major ingredient in the magnetic mineral. Do any of the other minerals you tested contain iron?

Question 10: Consider the minerals magnetite and hematite. Which factor do you think is most important in magnetism: chemical composition or crystal structure? Explain.

STATION4: The acid test

Materials at this station: Samples of quartz, feldspar, calcite, and chalcopyrite; a bottle of dilute (10%) Hydrochloric acid (about the same acidity as lemon juice). Please wash each mineral after testing and dry off before returning the mineral to the tray.

Question 11: Which mineral reacts strongly with acid (effervescences)?

Question 12: Look at the chemical formula of the mineral. Which gas do you think is released as it effervesces? Explain.

Question 13: Look at the chemical formulas of the minerals in the Table 1.2. Is there another mineral that could react by effervescing? Which one is it? Explain whether the remarks in the table support your idea?

STATION 5: Testing hardness of minerals

Materials at this station: Samples of quartz, gypsum, calcite, pyrite, chalcopyrite. Glass plate.

Question 14: The hardness of your fingernail is about 2.5 and the hardness of the glass plate is about 5.5 on the Mohs scale (p. 11). Try to scratch each of the minerals with your fingernail. Then CAREFULLY scratch each of the minerals on the glass plate, keeping the glass flat on the table. Fill in the names of each mineral in the blank next to its hardness, based on your observations (“H” means “hardness”; “<” means “less than”; “>” means ‘greater than”).

__________________ H <2.5. ___________________ 2.5 <H<5.5. _________________ H>5.5.

Question 15: Calcite, gypsum, and quartz are the Mohs hardness scale, which is given below. Fill in the names of the minerals you examined next to their exact hardness (bold).

1 –Talc 3 -- 5 – Apatite 7 -- 9 -- Corundum

2 -- 4 – Fluorite 6 – Feldspar 8 – Topaz 10 – Diamond

STATION 6: Mineral vs. mineral aggregates (rocks)

Materials at this station: Samples of calcite, calcite marble, olivine quartz.

Question 16: Determine whether each sample is a single grain (chunk) of mineral, or an aggregate of grains (p.2) and therefore a rock. Give your choice and your reason below.

Calcite -- Olivine –

Quartz -- Marble –

STATION 7: Determining cleavages on minerals

Materials at this station: Samples of amphibole (hornblende), muscovite, feldspar, quartz, and calcite.

Study the section of cleavage in your lab manual documents, particularly the figures. Then examine the specimens.

Question 17: Examine the minerals samples, determine the number of different cleavage planes for each one, and write that number in the blank below.

________Hornblende ________ Muscovite ________ Feldspar __________ Calcite

Question 18: For the samples above with more than one cleavage, look at the angle made by the intersection of adjacent cleavage planes. In the space below, write the names of the minerals and whether the angles between the cleavage planes are 90⁰ or not 90⁰.

Question 19: Examine the minerals in the round, plastic tray under the microscope to see the cleavage planes, which are shiny, flat, parallel surfaces. Which mineral breaks only along irregular fracture surfaces, rather than flat cleavage surfaces?

STATION 8: Estimating specific gravity of materials from the heft.

Materials at this station: Samples of galena, halite, feldspar.

Question 20: Read the section in your lab manual (p. 9) regarding the property of specific gravity and the qualitative measure of heft. Determine the heft of each sample as light, intermediate, or heavy, and write it next to the mineral name below.

_______________ Galena ________________ Halite __________________ Feldspar

Question 21: The mineral with intermediate heft has about average specific gravity for most minerals. For which of the minerals you examined is heft a diagnostic property (a property that helps distinguish the mineral from most others)? Explain.

Question 22: Both galena and halite have the same crystal structure. What accounts for their differences in specific gravity? Explain.

Reflection. Write a one-page reflection on this laboratory. Specifically consider how various combinations of mineral properties must be used to identify any given mineral, how this lab uses the scientific process, and how working collaboratively helped or hindered the successful completion of this assignment.