Properties of Minerals
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Questions and Answers

What is the primary reason why streak is often more reliable than the color of a mineral in its solid form?

  • Because the solid form is more difficult to find
  • Due to surface impurities or weathering (correct)
  • Because the powdered form is always darker
  • Because the solid form is always more vibrant

    • What tool is used to perform a scratch test to determine a mineral's hardness?

  • Steel file (correct)
  • Streak plate
  • Fingernail
  • Hammer

    • What is the primary purpose of the Mohs hardness scale?

  • To determine the number of cleavage directions in a mineral
  • To rank minerals based on their color
  • To determine the chemical composition of a mineral
  • To measure a mineral's resistance to scratching (correct)

    • What is the term for the way a mineral breaks along specific planes of weakness in its crystal structure?

    <p>Cleavage</p> Signup and view all the answers

    What is the result of a mineral with good cleavage breaking along its planes of weakness?

    <p>Flat, shiny surfaces</p> Signup and view all the answers

    What is the primary way to test the luster of a mineral?

    <p>By observing the mineral under a good light source</p> Signup and view all the answers

    What is the term for the way a mineral reflects light from its surface?

    <p>Luster</p> Signup and view all the answers

    Which of the following minerals is an example of one that exhibits perfect cleavage in one direction?

    <p>Mica</p> Signup and view all the answers

    What is the purpose of performing scratch tests using materials of known hardness?

    <p>To test the hardness of a mineral</p> Signup and view all the answers

    What is the term for the powder color produced when a mineral is dragged across a streak plate?

    <p>Streak</p> Signup and view all the answers

    Study Notes

    Mineral Properties and Testing

    • Minerals are naturally occurring, inorganic substances with a definite chemical composition and crystalline structure.

    Streak

    • Streak is the color of a mineral in its powdered form.
    • It is often more consistent and reliable than the color of the mineral in its solid form.
    • Testing method: Drag the mineral across a streak plate (unglazed porcelain) to produce a line of powder and observe the color of the streak.
    • Example: Hematite leaves a reddish-brown streak, while pyrite leaves a greenish-black streak.

    Hardness

    • Hardness measures a mineral's resistance to scratching.
    • It is determined using the Mohs hardness scale, which ranks minerals on a scale from 1 (talc) to 10 (diamond).
    • Testing method: Perform scratch tests using reference materials of known hardness (e.g., fingernail, copper coin, steel file).
    • Alternatively, try to scratch the reference material with the mineral.
    • Determine where the mineral falls on the Mohs scale based on which materials it can scratch and which materials can scratch it.
    • Example: Quartz has a hardness of 7 and can scratch glass, which has a hardness of about 5.5.

    Cleavage

    • Cleavage describes how a mineral breaks along specific planes of weakness in its crystal structure.
    • Minerals with good cleavage break smoothly along these planes, creating flat, shiny surfaces.
    • Testing method: Examine the mineral for natural planes of separation.
    • Gently tap the mineral with a hammer or use a knife to see if it breaks along flat surfaces.
    • Note the number of cleavage directions and the angles between them.
    • Example: Mica exhibits perfect cleavage in one direction, allowing it to split into thin sheets, while calcite has three directions of cleavage that form rhombohedral fragments.

    Luster

    • Luster refers to the way a mineral reflects light from its surface.
    • It can range from metallic and glassy to dull or earthy.
    • Testing method: Observe the mineral under a good light source.
    • Describe how the light interacts with the surface of the mineral using descriptive terms such as metallic, vitreous, pearly, resinous, or dull.
    • Example: Galena has a metallic luster, while quartz typically has a vitreous luster.

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