This paper deals with the relation between firing temperature and microstuctures of fractured, lapped and polished surfaces with their crystalline textures in steatite, forsterite, high and low alumina and mullite by the use of electron microscopy and etching technique. The results obtained are summarized as follows:
(1) Defects found on lapped and polished surfaces are 'pores' which occupy 6-20% in area.
(2) Crystal grains are not so much released in polishing of steatite, leading to the easy formation of gloss.
(3) The release of crystal grains on polished forsterite is caused by large thermal expansion and uneven distribution of grains.
(4) Pores in area increase as the firing temperature drops in high alumina.
(5) The rise of firing temperature causes the separation of the texture in grain boundaries, leading to the improvement of gloss in low alumina.
(6) Mullite becomes glossy easily in spite of a high porosity of 11%.
(7) The effect of firing temperatures upon the mechanical and structural properties becomes stronger in the order of low alumina, forsterite, high alumina and steatite, while it is not clear in mullite.
