Australian Facetors' Guild Limited

Orientation of Topaz

  • 12 Jul 2021 5:36 PM
    Message # 10745410

    I am trying to identify the C-axis in some river polished Topaz using a polariscope. Can someone please confirm that my understanding is correct.

    Turn polariscope until lens are at 90 degrees.

    Place stone on and locate axis where maximum light penetrates the stone.

    This is then the C-axis.

    Dop stone 7-10 degrees off this axis.

  • 16 Jul 2021 7:32 AM
    Reply # 10754389 on 10745410

    Don’t know the answer to that question Jim. Try the “Aussie Lapidary Forum” plenty of activity on there, should be someone there who can help.

  • 17 Jul 2021 12:47 AM
    Reply # 10756034 on 10745410

    With the polars crossed orient the stone until the stone does not go light and dark, mark this point.  Turn the stone over (i.e. end for end it) and again orient the stone until it does not go light and dark.  A line through the two points is the direction of the C axis.  In other words - A position of single refraction in a doubly refractive stone.  Might be easier to look for a line of colours if there is one - this is the cleavage plane.  Good luck.

    John Sellars

  • 25 Jul 2021 10:21 AM
    Reply # 10772649 on 10745410

    Thanks for the advice.

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