Dichroscope

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The dichroscope, also called Haidinger loupe (after its inventor Wilhelm Ritter von Haidinger ), is a special loupe for determining and testing minerals and gemstones . It uses the dichroistic or pleochroistic properties of the objects of investigation.

Structure and properties

Sectional drawing of a dichroscope

The dichroscope is basically designed like a small telescope . One side of the tube is closed with a lens , which also functions as a magnifying glass. Within the tube is a calcite - crystal fixed, the upcoming from the examination object light beam into two separate, adjacent, polarized light beams shares ( ordinary and extraordinary ray ).

Depending on how these light rays differ in color, the object can be assigned certain properties with regard to its crystal structure . It can happen that with certain crystals up to three different colors become visible if you turn it during the test.

Colours optical property Crystal structure
a color
Isotropic amorphous ( glass ), microcrystalline , cubic
two colors
Anisotropic , birefringent , optically uniaxial Trigonal , tetragonal , hexagonal
three colors in two different directions
Anisotropic, birefringent, optically biaxial Triclinic , monoclinic , rhombic

Different minerals show such strong pleochroism that you can see the different colors without a dichroscope. Above all, andalusite , burgerite , cordierite , dravite , epidote , schörl , tanzanite , titanite and uvite should be mentioned here .

meaning

Testing with a dichroscope is particularly important in the gemstone industry, as similar minerals cannot be differentiated by hardness or line color alone . For example, emerald and green-colored minerals of the tourmaline group have the same properties in terms of the properties mentioned above. In the dichroscope, however, the emerald shows a blue-green and a yellow-green field, while green tourmalines show a lilac-green and a black-green.

Glass always shows only one color in all directions, even with ingeniously inserted lead crystal rivers and gemstone cuts to imitate their fire.

history

The dichroscope was first presented to the public by Wilhelm Ritter von Haidinger in 1845 in Prague. The Nicol prism invented by William Nicol (1768–1851) is considered to be the forerunner of the dichroscope .

literature

  • HW Dove : The dichrooscope . In: Annals of Physics and Chemistry . tape 110 . Barth, Leipzig 1860, p. 265 ( digitized on Gallica ).
  • Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 49 .
  • Karl Krüger: The realm of minerals and rocks . Safari Verlag, Berlin 1974, p. 293 .

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