Device and Method of Optically Orienting Biaxial Crystals for Sample Preparation

Timothy Thomas¹, George R. Rossman², Mark Sandstorm³

¹Gemological Institute of America, 5355 Armada Dr., Carlsbad, California, USA  920085
²Division of Geological and Planetary Sciences, California Institute of Technology, MS 170-25, Pasadena, California, USA  91125
³Deliciously Nerdy Labs, 6170 W Lake Mead Blvd #461-1643, Las Vegas, NV 89108

    An optical device we refer to as the "biaxial orientation device" has been developed for finding the optical plane, acute bisectrix, and obtuse bisectrix in biaxial crystals by means of optically aligning conoscopically formed melatopes and measuring the angular coordinates of the melatopes, where the angular values allow for determination of the optical plane containing the optical axes using a vector algebra approach.  After determination of the optical plane, the apparatus allows for the sample to be aligned in the acute bisectrix or obtuse bisectrix orientations and to be transferred to a simple mechanical component for subsequent grinding and polishing, while preserving the orientation of the polished faces relative to the optical plane, acute bisectrix, and obtuse bisectrix during the grinding and polishing process.  Biaxial crystalline material samples prepared in the manner are suitable for accurate spectroscopic absorption measurements in the acute bisectrix and obtuse bisectrix directions as well as perpendicular to the optical plane.

Revised 2-May-2014