Patent ID: 7297645

Claim:
An opalescent glass ceramic which is devoid of ZrO 2 and TiO 2, and which comprises an Me(II)O component in an amount of less than 4% by weight, and an Me(IV)O 2 component in an amount of 0.5 to 3% by weight, the glass ceramic consisting essentially of: Component % by weight SiO 2 55-62 Al 2 O 3 13≦-17 B 2 O 3 0-2 P 2 O 5 1.5-3 Li 2 O 0-2 Na 2 O 7-12 K 2 O 8-12 MgO 0-2 CaO 1-<4 BaO 0-2 Tb 2 O 3 0-3 Me(IV)O 2 0.5-3 wherein said Me(IV)O 2 consists essentially of 0<CeO 2 ≦1 and 0<SnO 2 ≦2.5, and wherein the glass ceramic has a thermal expansion coefficient (TEC) in the range of 9.0-13.5×10 −6 /K.