OPTICMIN©: AN ONLINE TEACHING TOOL FOR MINERAL IDENTIFICATION IN THIN SECTION

The hours of teaching optical mineralogy or the identification of minerals in thin sections and the nomination of rocks based on their paragenesis and texture has been reduced in the undergraduate class schedule over the last decades. Nevertheless, skills in optical mineralogy remain still essential in Earth Sciences, not only in academia, but also in the applied the Earth Sciences, such as mineral exploration, asbestos or material characterization in general.

The open access OPTiCMin^© software was developed to help students to acquire the essential optical parameters crucial for the identification of minerals in thin section. The mineral data base contains so far the optical characteristics of the 141 most frequent minerals and is based on the experience of teaching optical mineralogy and metamorphic petrology over the last 15 years. A microscopy room with 21 working places was set up, each equipped with a stereomicroscope and a polarized light microscope coupled to a computer and a camera. A tablet allows the projection from every working place on a central screen promoting interactive microscopic work. Students as well as teachers have become more active and enthusiastic by using the new tools.

The optical parameters of the minerals were grouped and summarized in eleven entries or columns. They include the mineral name/formula, color/pleochroism, form/habitus, cleavage, twinning, extinction/elongation, birefringence, relief/refractive indices, optical character/crystallographic system, optical angle and occurrence/paragenesis/alteration. The program provides also first thin section images for the most frequent minerals with characteristic features, the bird’s eye in biotite or the typical amphibole cleavage.

The short introduction at the beginning of the Website explains the terms and abbreviations. The search engine will only find the words reserved for the corresponding optical property. At the end of every column, there is a box where you enter the observed optical parameter. For example, the user may enter the color “blue” and the optical character is negative “U(-)”. The program will provide a first table with the minerals that meet the criteria. The user may then continue to determine further optical properties to shorten the list of possible results as well as consult the bibliography of optical mineralogy.