Craig Robert Walton 

Mineral identification using an optical microscope forms a key part of every introductory course in Earth Sciences. The presence or absence of particular minerals and their textural relationships to one another - that is, the visual impression of the size, shape, and arrangement of grains/crystals/particles in a rock - act as keys to the origin and evolution of the Earth system. Indeed, many would claim that the best geologists have simply seen the most rocks (/minerals). Whilst this is no longer strictly true in an age of increasingly abstracted geochemical and statistical approaches, optical microscope studies will (or at least should) remain at the heart of geology for the foreseeable future.

So we come to colour-blindness and visual impairment in optical microscopy. A reasonable percentage of the population are colour-blind or visually impaired. Nowadays, plenty of tools exist to level the playing field and help both tutors and students to see eye-to-eye. This document attempts to make systematic use of those tools.

In Chapter 1, I briefly review some essential points to bear in mind when approaching rock forming mineral classification, which together help to shrink a complicated problem (whether colour blind or not) down to something more tractable. In Chapter 2, I lay out several systematic approaches for mineral and rock classification. In Chapter 3, I present collected optical microscope images of common rock-forming minerals in plane polarised light (PPL) and cross polarised light (XPL). Using the Color Oracle software, I try to capture how the same images would appear to individuals with differing types of colour blindness. Throughout, the goal is to develop a framework of 'universal' diagnostic mineral features in thin section, i.e., features that should be both possible to identify for a broad range of individuals, and possible to describe using language that translates directly from one person to another.