A glass ceramic contains the following components by wt %: 60 to 80% of SiO2; 4 to 20% of Al2O3; 0 to 15% of Li2O; more than 0 but less than or equal to 12% of Na2O; 0 to 5% of K2O; more than 0 but less than or equal to 5% of ZrO2; 0 to 5% of P2O5; and 0 to 10% of TiO2. A crystalline phase contains at least one of R2SiO3, R2Si2O5, R2TiO3, R4Ti5O12, R3PO3, RAlSi2O6, RAlSiO4O10, R2Al2Si2O8, R4Al4Si5O18, quartz and quartz solid solution. With a liquidus temperature below 1,450° C., a thermal conductivity above 2 w/m·k, and a Vickers hardness above 600 kgf/mm2, the glass ceramic is applicable to portable electronic devices and optical devices.