The present invention relates to a process for preparing a glass-ceramic body comprising the steps of providing a basic glass body and subjecting the basic glass body to a thermal treatment whereby a crystalline phase embedded in a glass matrix is formed. According to the invention, the basic glass body is made of a composition comprising 65 to 72 wt-% SiO2, at least 10.1 wt-% Li2O and at least 10.1 wt-% A1203 based on the total weight of the composition, the proportion of Li2O to Al2O3 being from 1:1 to 1.5:1. The thermal treatment involves a nucleation step followed by several crystallization steps at different temperatures, whereby at least two different crystalline phases are formed.
