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Sample Paper - ALTA Metallurgical Services

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Sample Paper - ALTA Metallurgical Services

    Mineral Lab part 1

    GLS100 Lab - Mineral Properties

    Physical Geology Dr. Lindley S. Hanson

    PART I

     What is a mineral?

    A mineral is naturally occurring, inorganic, homogeneous solid with a characteristic

    chemical composition, and ordered atomic arrangement. In order for a substance to be

    labeled a mineral all of these criteria have to be true.

    Explanation:

    1. Naturally occurring: Formed by natural processes (not created in a laboratory).

    2. Homogeneous solid: A mineral consists of a single solid compound or element, which cannot be physically subdivided into other chemical components.

    3. Inorganic: Not created by organisms or from their remains. This qualification excludes those substances, which are solely a product of organic activity (e.g. sugar) and not

    substances, which are commonly inorganic but may be precipitated by organisms (i.e. calcite).

    4. Characteristic chemical composition: This signifies that a mineral can be represented by a specific chemical formula.

    5. Ordered Atomic Arrangement: The atoms forming a mineral are arranged in a geometric pattern, which persists throughout the entire mineral. All minerals by definition are crystalline. Substances in which atoms are randomly arrange are called amorphous. All glasses by definition are amorphous.

    Note: A mineraloid is a solid, which has all the properties of a mineral except that it has no ordered atomic arrangement and has a slightly variable chemical composition. Two common mineraloids are limonite (rust) and bauxite (major ore of aluminum).

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    Mineral Lab part 1

    EXERCISE 1: Is it a mineral?

    In table 1 are eight common substances. Review each property discussed above and

    determine whether or not each solid would be considered a mineral. If you think a

    substance would not be considered a mineral then state why.

    Table 1. Which are minerals and which are not?

    Material yes/no Explanation

    volcanic glass

    sugar

    rust (limonite)

    ice

    steel

    coal

    salt (halite)

    cubic zirconium

    Part II

    Mineral Properties and Identification

    Each mineral has a unique set of physical properties from which it can be readily

    identified. The physical properties that you will need to know are:

    1. Luster 5. Color

    2. Cleavage, Fracture and 6. Streak Parting

    3. Crystal form 7. Tenacity

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    Mineral Lab part 1

    4. Hardness 8. Specific gravity

    There are many other physical properties, such as magnetism, crystal form, habit (mode of occurrence), and diaphaneity (transparency), that may be useful in mineral identification.

    EXERCISE 1

    Luster is the measure of the quality or intensity of reflected light. When identifying luster it is important to look at unweathered, freshly broken surfaces; in particular, cleavage surfaces. The materials listed below (table 2) are used to define the different types of luster.

    Table 2. Lusters used to describe minerals.

    Type of luster Appearance Examples

    metallic Like that of metal gold, silver, copper

    adamantine Like that of diamond diamond

    vitreous Like that of glass fluorite, quartz, mica

    greasy Like that of grease quartz

    pearly like that of pearl mica, talc

    waxy like that of wax serpentine, talc

    dull like that of chalk clay

    State the luster(s)* exhibited by each specimen listed in table 3. These minerals are labeled L1-L6 in the mineral drawers found in the gray cabinet in the back of the lab.

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    Mineral Lab part 1

    Table 3. Luster exercise.

    # Mineral Luster(s)

    L1 galena

    L2 muscovite

    L3 kaolinite

    L4 pyrite

    L5 talc

    L6 quartz

*Note: Some minerals have only one characteristic luster while others may have two or

    more. For example, the mineral hematite may be metallic or dull and the mineral gypsum may be vitreous to pearly.

    EXERCISE 2: Cleavage, Fracture, Parting, and Habit

Cleavage is the splitting of a mineral along

    one or more inherent planes of weakness. The inner atomic structure of a mineral governs whether or not the mineral will

    cleave, and the type of cleavage it displays. Cleavage is easily demonstrated with the structure of graphite (fig. 1.1). The lines

     between the carbon atoms represent the bonds holding the atoms together. The longer Figure 1.1. Structure of the line the weaker the bond. graphite.

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    Mineral Lab part 1

    Can you determine how this mineral will

    break?

    Cleavage: The flat shiny surfaces that are produced when a mineral cleaves are called cleavage planes. A mineral may exhibit 1,2,3,4, or 6 (rare) different directions of cleavage. (Note: Planes that are parallel are not considered different cleavage directions.) The different types of cleavage are described in the Table 4.

    Table 4. Types of cleavage.

    Type of Description Examples Cleavage

    1 plane of cleavage. Forms flat muscovite, biotite, talc, Pinacoidal fragments or flakes with ragged chlorite, graphite edges.

    2 planes of cleavage.(Often the feldspars, amphiboles, Prismatic most difficult cleavage to identify.) pyroxenes

    3 planes of cleavage intersecting Cubic halite, galena at right angles.

    3 planes of cleavage not Rhombic gypsum, calcite intersecting at right angles.

    4 planes of cleavage. (Forms Octahedral fluorite triangular cleavage faces)

    Fracture is any break other than cleavage. The break does not yield a smooth and flat surface as with cleavage. Fracture occurs when bonds between atoms are more equal in

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    Mineral Lab part 1

    strength and breakage is random. In the absence of cleavage, the fracture (table.5) is

    identified.

    Exercise 2a: Cleavage

    Five mineral fragments produced by breakage are illustrated in Figure 1.2. Identify the cleavage that is exhibited by each and fill in the blanks below.

1. ____________________________

    2. ____________________________

    3. ____________________________

    4. ____________________________

    5. ____________________________ Figure 1.2. Fragments formed by the

    cleavage of five different minerals

Table 5. Types of fracture

    Type of fracture Description

    conchoidal Fracture yields a smooth, often shiny, curved surface

    subconchoidal Moderately smooth, curved surface

    uneven Fracture yields a rough, irregular surface

    Parting and habit

    Crystalline aggregates: Some minerals have a particular mode of occurrence or habit;

    they may typically occur as granular, fibrous, or platy crystalline aggregates. The term

    granular refers to aggregates of small equant crystals. For example the mineral olivine

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    Mineral Lab part 1

    occurs in granular aggregates. As shown in figure 3, crystalline aggregates generally display a characteristic parting or fracture.

    Crystalline aggregates exhibit parting, similar in appearance to cleavage, but unlike cleavage, occurs between individual crystals, rather than through them. Examples (Figure 3) are shown below.

    Examples of partings and habits

     1. fibrous parting: Asbestos

    occurs in fibrous

    aggregates of crystals.

    2. basal parting: Corundum

    parts between crystals

    that are in a column.

    3. flaky parting: Graphite,

     chlorite, and talc typically

    occur in aggregates of Figure 3. Partings and modes of occurrence

    small platy crystals that (habit).

    flake off from the mineral

    aggregate.

    The term massive is commonly used to describe aggregates of microscopic or

    cryptocrystalline crystals forming a compact featureless mass with no preferred parting. Kaolinite, quartz (var. chert), pyrite, and hematite often occur in massive aggregates. The luster and breakage of a mineral aggregate may be different than that of the individual mineral crystal.

    NOTES:

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    Mineral Lab part 1

    Exercise 2b: Cleavage and Fracture

    Fill out table 6. For specimens labeled C1-C8, identify the cleavage and then briefly

    describe the mineral (e.g. color, luster, etc.). For specimen F9 and F10, identify the

    fracture and then describe the sample. (F10 is a volcanic glass and is therefore not a

    mineral.)

    Table 6 Cleavage and fracture exercise.

    # Mineral cleavage/fracture Description

    Cl gypsum

    C2 calcite

    C3 muscovite

    C4 galena

    C5 fluorite

    C6 orthoclase (feldspar)

    C7 halite

    C8 hornblende (amphibole)

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    Mineral Lab part 1

    F9 chalcopyrite

    F10 obsidian

    Crystal Form

    When minerals grow in an unrestricted environment (i.e. rock cavity) they obtain geometric shapes which reflect their inner atomic arrangement. Such perfectly shaped forms are euhedral crystals (fig. 4) and each mineral displays a unique crystal form which can aid in its identification. This euhedral crystal is what most people think of as a crystal. However, geologist use the term crystal in a more general sense; a crystal is any single mineral grain that makes up a crystalline rock. Typically, growing crystals interfere with one another and become distorted and malformed. When crystals are anhedral or subhedral the mineral's crystal form is generally not identifiable.

Minerals that commonly occur as

    euhedral (well shaped) crystals are:

1. quartz (trigonal)

    2. fluorite and pyrite (cubic)

    3. garnet (dodecahedral)

    4. gypsum (rhombic)

    5. fluorite (octahedral)

Note: the terms cubic, rhombic and Figure 1.4. Examples of crystal forms.

    octahedral are also used to describe

    cleavage. To avoid confusion state what

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    Mineral Lab part 1

    you are referring to when using these

    terms.

    EXERCISE 3: HARDNESS

    Hardness is a mineral’s resistance to abrasion and is a measure of the bond strength between atoms. The stronger the interatomic bonds the harder the mineral.

    Determination of hardness: Hardness is determined by comparing the hardness of the mineral in question with that of a mineral from Moh’s Hardness Scale (Table 1.7), or with another object of known hardness (relative to Moh’s Scale).

    For this exercise use the plastic boxes labeled “hardness exercise” that contain minerals

    1-9 on Moh’s Hardness Scale. The number on each mineral specimen does not correspond to its hardness. However, by determining the relative hardness of the nine minerals you can identify them.

    Procedure:

    1. Use a glass plate (H=5.5) to separate the minerals into two groups (<5.5

    and >5.5).

    2. Determine the relative hardness of the minerals by comparing them with each

    other. Your fingernail (H-2.5) will help with those minerals < 5.5.

    3. In Table 1.6, place the number of each specimen where it belongs relative to

    the hardness scale. Once you have done that you have identify the minerals.

    Table 1.7. Moh's hardness scale and hardness exercise

    Moh's Scale of Hardness

    Hardness Mineral Sample # Object (H)

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