Chapter 12.4 Birefringence and Pleochroism

Chapter 12.4 Birefringence and Pleochroism

Birefringence and Pleochroism 101 Chapter 20.3 contains a more complete explanation of dichroscopes, including instructions on how to build your own for under two dollars. Figure 12-13 Pleochroism is a po- larization phenomenon, here seen with !sherman’s sunglasses and a tourmaline crystal with a closed c- axis. To see the e"ect, you need to hold the stone in front of an intrin- sically polarized light source, such as a #at screen display or the blue sky 90° from the sun. Figure 12-14 Operating principle of a simple calcite birefringent polariscope, or dichroscope. Light rays from below enter the crystal and split according to polarization, taking di"erent paths (a). If oriented properly, an input window on one side of the crystal will produce two output windows, one for each polarization (b). Trimmed to a convenient size (c) and mounted in a sturdy holder (d), the calcite crystal becomes a dichroscope, which can be held against a sample of gem rough to identify the optical axis and dominant body colours. 12.4.1 Gem Design and Orientation for Pleochroism In addition to providing a fun little example of seemingly magical physics, dichroism and trichroism have a direct impact on the appearance of a gemstone. For example, some tour- malines display complete absorption along one axis of the crystal – a phenomenon often referred to as a “closed c-axis.” Viewed along their length, such stones are opaque black, hardly an appealing colour for a gem. Other samples may show a pleasing green or turquoise colour in one direction, and a considerably less aesthetic brownish-green along an- other (see Figure 6-26). There are design and orientation choices which can help you get the most out of pleochroic gemstones. Turn to Chapter 6.7.1 for practical advice. Figure 12-15 A pleochroic tourmaline showing yellow-green colours along the up-down direction and pale blue-green left and right...

View Full Text

Details

  • File Type
    pdf
  • Upload Time
    -
  • Content Languages
    English
  • Upload User
    Anonymous/Not logged-in
  • File Pages
    1 Page
  • File Size
    -

Download

Channel Download Status
Express Download Enable

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

  • Not to be reproduced or distributed without explicit permission.
  • Not used for commercial purposes outside of approved use cases.
  • Not used to infringe on the rights of the original creators.
  • If you believe any content infringes your copyright, please contact us immediately.

Support

For help with questions, suggestions, or problems, please contact us