Mineral identification II and Exsolution

Lab groups:

Instructions for this exercise

The main goal of this lab is introducing you to the first set of minerals you will learn about in detail. In the last lab, you learned (and taught) a number of techniques that you can use to differentiate minerals from each other. In this and the next few labs you will use these techniques to make a catalog from which you can study.

Your task is to learn the important features of each mineral. One important feature of every mineral is its chemical composition. Most geologists, in identifying a mineral, will ask what other minerals it was found with, or what rock type it was found in. This is because minerals that form together frequently share aspects of their chemistry.

 

à           Before you come to lab, you should you should therefore record the following for each mineral on a separate sheet of paper (look the info up in your text).

1.     Name

2.     Chemical formula (if the formula is complex, then only the elements, not their proportions – see below)

3.     Geologic occurrence (not locations, but environments. e.g., Pyrite – sulfide ore deposits)

4.     Typical crystal shape, size and state of aggregation.

5.     Identifying Characteristics. This is the key. What is it important to know about this mineral to be able to identify it? To distinguish it from most minerals is easy, but what about minerals that share many features? (i.e., for pyrite, the important features are not those that distinguish it from quartz, but those that distinguish it from chalcopyrite – see Plate II in your text)

What you will turn in:

1.     A sheet for each mineral in your topic that includes notes made based on your lab observations, particularly those techniques most useful in identifying that mineral.

2.     Notes taken during lab on the minerals in the other topics (these do not have to be comprehensive - we will be compiling the sheets into a reference book).

3.     Individual work on topics D & E.

Cooperative strategy:

We will be doing a group exercise. You are a member of a team (1-5), and you must become an expert on a topic (A-C). You will develop answers to your topic material first on your own (at home, using your text), then you will share your answers with the other experts on that topic from the other 5 teams. Finally, we will go through four rotations in which each expert will teach their topic to the other members of their team.

Each team will turn in a single lab report, but you are responsible for knowing all the material in this lab. In addition, you must critically review the results of the other experts on your team while they are teaching.

Topic A, Mineral Identification - Oxides & Hydroxides

Using your text and any other reference materials you wish, learn to identify the following minerals and distinguish them from similar ones.

à           Corundum	à           Hematite	à           Magnetite
à           Rutile	à           Goethite ("Gur-tight" is a near pronunciation)	à           Chromite

 

Topic B, Mineral Identification - Halides & Sulfides

Using your text and any other reference materials you wish, learn to identify the following minerals and distinguish them from similar ones. Turn in a sheet with the four items mentioned above for each mineral.

à           Ulexite	à           Halite	à           Fluorite (yes, it's "uo". don't spell it wrong!)
à           Barite	à           Gypsum

 

Topic C, Mineral Identification - Carbonates

Using your text and any other reference materials you wish, learn to identify the following minerals and distinguish them from similar ones. Turn in a sheet with the four items mentioned above for each mineral.

à           Calcite	à           Siderite	à           Rhodochrosite
à           Aragonite	à           Dolomite	à           Malachite
à           Azurite

Topic D (individual), Mineral Questions

à           Corundum: What turns run-of-the-mill corundum into sapphire or ruby?

à           Hematite: Is it magnetic? What color is its streak?

à           Magnetite: This is a spinel-group mineral, meaning it has the same structure as spinel. Spinel group minerals can be either normal, or inverse. Which is magnetite? Describe. Magnetite is critical for paleomagnetic studies. It is ferrimagnetic. Describe or sketch the difference in alignment of spin directions between ferromagnetism and ferrimagnetism (consult Klein).

à           What is the difference, chemically, between gypsum and the closely-related mineral anhydrite. How does this apply to constructing sidewalks? (Hint: When you mix up a batch of concrete, you have to add water. Where does the water go?)

à           Is Aragonite stable at the Earth’s surface, according to Klein (Fig. 4.16, p.120)? What is the most common source of aragonite (hint: biogenic)?

 

Topic E (individual), Exsolution

Samples 10-2-6 and 10-2-31 are Alkali Feldspar. They show perthitic texture, and so could also be called perthite. Look this up in your book to find out more about it.

à           Sketch the perthitic texture, labeling the two different compositions. It would be best to sketch it as it appears in your hand lens.

à           Explain how the texture formed, preferably including a schematic T-X diagram (i.e., don’t try to find one that actually has the correct numerical values for perthite)

à           Sample 10-2-21 is also Alkali Feldspar. Why does it not display the same features?

 

Sample 10-2-53 is Graphic Granite. Look this term up in your text.

à           Sketch this texture as it appears in this hand sample without your hand lens. Label the two prominent minerals.

à           Does this texture form in the same way as perthite?