The temperature-dependent optical activity of quartz: from Le Châtelier to chirality measures

Quartz, the most abundant mineral in Earth's crust, is a chiral crystal. It was the first material for which the phenomenon of the optical rotation was observed. In the late 19th century/beginning of the 20th, several researchers, the most famous of which is Le Châtelier, investigated how this optical rotation changes with temperature. By employing a modern analytical/computational tool for evaluating the degree of chirality on a continuous scale, we were able to show a remarkable agreement between the original optical rotation/temperature curve, and the chirality/temperature curve. We thus provide a direct interpretation of the early observations, as reflected in the dependence of the optical rotation of the degree of chirality, linking these two properties quantitatively.