MACHINABLE AND CHEMICALLY TOUGHENABLE GLASS CERAMIC

The present invention is directed to a kind of machinable glass ceramic which can be chemically toughened. The machinable and chemically toughenable glass ceramic, which comprises, as represented by weight percentage based on the following compositions, 25-75 wt % of SiO2, 6-30 wt % of Al2O3, 0.1-30 wt % of Na2O, 0-15 wt % of K2O, 0-30 wt % of B2O3, 4-35 wt % of MgO, 0-4 wt % of CaO, 1-20 wt % of F, 0-10 wt % of ZrO2, 0.1-10 wt % of P2O5, 0-1 wt % of CeO2 and 0-1 wt % of SnO2, wherein P2O5+Na2O>3 wt %, and Al2O3+Na2O+P2O5>17 wt %. Mica crystalline phase can be formed in the glass ceramic and the glass ceramic can be chemically toughened by one step, two steps or multiple steps with depth of K-ion layer of at least 15 μm and surface compress stress of at least 300 MPa. The profile on depth of the ion exchange layer follows the complementary error function. Hardness can be improved by at least 20% after chemical toughening. The dimension deviation ratio is less than 0.06% by ion-exchanging.