Practice For Exam 2

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Online Practice Test  #2  pretty tacky, eh?

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  1. Pleochroism in gems is caused by

    absorption of different wavelengths of light in different directions.
    the presence of more than one chromophore.
    the absence of an optic axis.

  2. The amount of bending light undergoes when passing through a gem or mineral depends on

    a) the angle at which it enters.
    b) the refractive index of the gem or mineral.
    c) the wavelength (color) of the light.
    d) all of the above.
    e) b and c.

  3. Dispersion is

    a) a phenomenon that produces play-of-color.
    b) an optical property that can be measured with a refractometer.
    c) related to the difference in the speed of red and blue light in a gem or mineral.
    d) something that only occurs in anisotropic materials.
    e) b and c

  4. A polariscope tests for

    refractive index.
    the presence of chromophores.
    none of the above

  5. A refractometer can be used to measure

    a) refractive index.
    b) birefringence.
    c) optic sign.
    d) pleochroism.
    e) a, b and c

  6. A dichroscope is used to check for


  7. A mineral's critical angle is the angle at which

    light exiting the mineral is internally reflected.
    light entering the mineral is refracted to 40o.
    light exiting the mineral is refracted parallel to the surface of the mineral.
    light exiting the mineral is refracted away from the normal.
    none of the above.

  8. The refractive index of a substance describes

    how strongly light is bent by the substance.
    whether a substance can polarize light.
    whether a substance can split light into two plane polarized rays.
    the amount of diffraction occurring within a substance.
    all of the above.

  9. Optically anisotropic minerals differ from isotropic minerals by

    having low critical angles.
    being able to polarize light.
    having high critical angles.
    being fluorescent in ultraviolet light.
    none of the above.

  10. Light within a gemstone that strikes a facet at an angle less than the critical angle of the gem will

    exit the gem.
    be internally reflected.
    be refracted parallel to the facet.
    be split into two plane polarized rays.
    none of the above

  11. Light that travels through an anisotropic material is always

    split into 2 rays
    doubly refracted
    none of the above

  12. Light that travels through an isotropic material is always

    split into 2 rays
    doubly refracted
    none of the above

  13. A gem that looks black every 90o of rotation in a polariscope must be

    monoclinic or triclinic
    hexagonal or tetragonal
    none of the above

  14. An optic axis is defined as a unique direction in a mineral along which light

    will be split into two rays
    will be polarized into two directions
    will pass through without being split or polarized
    will be most strongly absorbed
    none of the above

  15. A mineral that is trichroic must

    be isotropic
    be isometric (cubic).
    be triclinic.
    in some orientations blink from dark to light when rotated in a polariscope.
    none of the above.

  16. A pleochroic mineral must always be

    none of the above.

  17. A gem that shows two distinct shadow edges on a refractometer must always be

    none of the above

  18. Double refraction is visible in some gems as

    a doubling of pavilion facet junctions when viewed through the table.
    oriented inclusions.
    total internal reflection
    none of the above

  19. A gem that is dichroic will

    have one or two optic axes.
    have more than one refractive index.
    be anisotropic.
    be a member of either the hexagonal, tetragonal, monoclinic, triclinic or orthorhombic crystal system.
    all of the above.

  20. A transparent material will only refract light if

    it is anisotropic
    it has a birefringence
    it can polarize light
    the light enters at greater than 0o to the normal
    all of the above

  21. The shadow edge of the extraordinary ray in a refractometer can

    move as the gem is rotated.
    be less than the shadow edge of the ordinary ray.
    be greater than the shadow edge of the ordinary ray.
    overlap the shadow edge of the ordinary ray if the birefringence is low.
    all of the above

  22. The flashes of color that are characteristic of a diamonds brilliance are caused by

    double refraction
    total internal reflection

  23. Dull, lifeless, gemstones that show little brilliance are sometimes a consequence of culet angles that are

    1 or 2o greater than the critical angle for the gem material.
    less than the critical angle for the gem material.
    equal to the normal.
    less than the reflective angle for incoming light through the table.
    too shallow for a properly cut crown.

  24. Internal reflection within a gemstone occurs when light strikes a facet at

    greater than the critical angle
    less than the critical angle
    the critical angle
    an angle parallel to the normal
    parallel to the optic axis

  25. Pleochroism is possible in gems of the

    hexagonal system
    triclinic system
    monoclinic system
    tetragonal system
    all of the above

Updated 08/22/16
Comments and questions to
Department of Geological Sciences
The University of Texas at Austin