Polychromatic polarization: Boosting the capabilities of the good old petrographic microscope

Bernardo Cesare,Michael Shribak,Nicola Campomenosi

doi:10.1130/g49303.1

Abstract

Abstract Polychromatic polarizing microscopy (PPM) is a new optical technique that allows for the inspection of materials with low birefringence, which produces retardance between 1 nm and 300 nm. In this region, where minerals display interference colors in the near-black to gray scale and where observations by conventional microscopy are limited or hampered, PPM produces a full spectrum color palette in which the hue depends on orientation of the slow axis. We applied PPM to ordinary 30 µm rock thin sections, with particular interest in the subtle birefringence of garnet due both to non-isotropic growth or to strain induced by external stresses or inclusions. The PPM produces striking, colorful images that highlight various types of microstructures that are virtually undetectable by conventional polarizing microscopy. PPM opens new avenues for microstructural analysis of geological materials. The direct detection and imaging of microstructures will provide a fast, non-destructive, and inexpensive alternative (or complement) to time-consuming and more costly scanning electron microscope–based analyses such as electron backscatter diffraction. This powerful imaging method provides a quick and better texturally constrained basis for locating targets for cutting-edge applications such as focused ion beam-transmission electron microscopy or atom probe tomography.

Highlights

The polarizing microscope is the fundamental analytical tool for any first characterization of geological materials
Polychromatic polarizing microscopy (PPM) is a new optical technique that allows for the inspection of materials with low birefringence, which produces retardance between 1 nm and 300 nm
We show how PPM, implemented as a complementary accessory on petrographic microscopes, allows unprecedented imaging of microstructures in very low birefringence minerals using standard 30 μm thin sections

Summary

Introduction

The polarizing microscope is the fundamental analytical tool for any first characterization of geological materials. ABSTRACT Polychromatic polarizing microscopy (PPM) is a new optical technique that allows for the inspection of materials with low birefringence, which produces retardance between 1 nm and 300 nm.

Results

Conclusion