Phase-polarisation data for the asteroids (45) Eugenia, (210) Isabella, (419) Aurelia and (704) Interamnia, all of them belonging to the F taxonomic class. The meaning of the symbols is the same as in Fig. 1. The vertical lines at the phase angle of 20° (corresponding to the typical value of the polarisation inversion angle of most asteroid taxonomic classes) are drawn as a reference to illustrate the anomalously low values of the inversion angle characterising this taxonomic class (see text).