EXCELIBR: An Excel Spreadsheet for Solving the Optical Orientation of Uniaxial and Biaxial Crystals
THE MICROSCOPE
2017, Volume 65:4, pp. 147–152
DOI
https://doi.org/10.59082/KLWH2345
AUTHORS
C.J. Steven and M.E. Gunter
ABSTRACT
The polarized light microscope remains the single most useful tool in identifying minerals. Using a spindle stage, a user can orient a crystal’s principle refractive index (RI) vectors, parallel to the lower polarizer, and in turn, observe its RI. Finding the principle RI vectors is accomplished by using either conoscopic methods, or more simply, using extinction data as inputs in the program EXCALIBR, which was developed by Bloss and Riess in 1973 (1). The use of EXCALIBR has major advantages over conoscopic methods, but it is hindered by interface and compatibility issues. Presented here is a Microsoft Excel spreadsheet named “EXCELIBR,” which performs similar functions to EXCALIBR, including solving for the optical orientation of biaxial or uniaxial minerals using extinction data. Using Excel as the interface, EXCELIBR is accessible, familiar, and versatile for the user. The program is useful for preliminary screening of a crystal for X-ray studies, optical characterization of minerals, and rapid mineral identification. Included with its crystal-orienting calculations are tabs for double variation and RI modeling, similar to those in Opt_cal, a program that calculates miscellaneous optical properties of minerals.