EXCELIBR: AN EXCEL SPREADSHEET FOR SOLVING THE OPTICAL ORIENTATION OF UNIAXIAL AND BIAXIAL CRYSTALS

The polarized light microscope remains the single most useful tool in identifying minerals. Using a spindle stage, a user can orient a crystal in 3-dimensions to locate principle vibration directions. Given a crystal with clearly defined crystallographic axes, the coordinates of crystallographic directions can also be located and related to the orientation of a crystal’s principle vibration directions. Finding the principle refractive index vectors is accomplished by using either conoscopic methods, or more simply, using extinction data as inputs in the program EXCALIBR. The use of EXCALIBR has major advantages over conoscopic methods but is hindered by interface and compatibility issues. Presented here is an Excel spreadsheet that performs similar operations to EXCALIBR, including solving for the optical orientation of biaxial or uniaxial minerals using extinction data. Using Microsoft Excel as the interface, the program is accessible, familiar, and versatile for the user. This spreadsheet is useful for optical characterization of minerals, rapid mineral identification, and for preparing samples for orientation-dependent analysis. Included with crystal orienting calculations are also tabs for double variation and refractive index modeling.