Abstract
Lattice constants and space group of low tridymite of type M dtermined here are: orthorhombic; a=9.940A, b=17.21A, c=40.92A; space group C2221. The long period in the c-direction is caused by minor transverse displacements of constituent atoms along (0 0.1), which simulatneously form the double period in the a-direction, both associated with the phase transition of tridymite.
