Abstract: Micaceous-cordierite-glass ceramic particularly suitable for stomatological, head surgery and neck surgery applicatiosn has a fracture toughness K.sub.IC of up to 2.0 MPa m.sup.1/2, a hardness HV.sub.0.07 of 300-1000, a compressive strength of up to 450 N/mm.sup.2, a linear thermal expansion coefficient of 75-125.times.10.sup.-7 K.sup.-1, good chemical stability and excellent machinability as well as a high resistance to wear and comprises a composition in weight percentages of______________________________________ SiO.sub.2 43-50 Al.sub.2 O.sub.3 26-30 MgO 11-15 R.sub.2 O 7-10.5 F.sup.- 3.3-4.8 Cl.sup.- 0.01-0.6 CaO 0.1-3 P.sub.2 O.sub.5 0.1-5 ______________________________________wherein R.sub.2 O is the sum of 3 to 5.5 wt. % Na.sub.2 O and 4 to 6 wt. % K.sub.2 O, a first crystal phase of mica, and a second crystal phase of 5 to 30 volume % cordierite, wherein relatively large mica crystals of 10 to 200 .mu.m are embedded in the glass and cordierite crystals of 0.5 to 5 .mu.m are arranged in the glass.

Abstract: A phosphate glass ceramic which can be utilized especially as biomaterial in medicine and biology. The object of the invention is to provide a glass ceramic extensively adapted to bone, possessing adjustable biologically active characteristics. Another object of the invention is to produce a glass ceramic free of SiO.sub.2 or low in SiO.sub.2, of high P.sub.2 O.sub.5 and CaO content, possessing adjustable biologically active characteristics. The object is solved, whereby an initial glass of the composition having the mass percentages of Al.sub.2 O.sub.3 3-21, CaO 8-26, R.sub.2 O 10-25, P.sub.2 O.sub.5 43-58, is provided under the condition that R.sub.2 O can contain up to 25% of mass of Na.sub.2 O and up to 18% of mass of K.sub.2 O, and is thermally treated after melting, to provide the new phosphate glass ceramic. The main crystal phases are apatite and aluminiumorthophosphate. The phosphate glass ceramic can contain additions of SiO.sub.2, B.sub.2 O.sub.3, F.sup.-, MgO, FeO, Fe.sub.2 O.sub.3, TiO.sub.2.