ON THE POLAR HABIT OF CRYSTALS OF POTASSIUM TETRATHIONATE, K2S4O6

The F forms, as defined by the Periodic Bond Chain Theory, of K2S4O6 w ith space group Cc have been derived from the crystal structure. When each F form is characterized by the indices {nh, nk, nl} of its slice thickness d(nh, nk, nl) and when polarity is disregarded, the F forms are in decreasing order of d(nh. nk, nl): {200}, {110}, {111BAR}, {111 }, {400}, {310}, {311BAR}, {002}, {202BAR}, {311}, {202}, {402BAR}, {3 12BAR}, {312} and {402}. The description as given by Groth (Chemische Krystallographie, Vol. II, p. 717) contains several errors. A new desc ription is given. The observed forms are all F forms. To explain the p olar habit the hypothesis is made that the dehydration of the cations determines the growth rate of a face. This hypothesis leads to the pre diction that {202BAR} should be present at the positive end of the c a xis and {311BAR} at the negative end. This agrees with the observation s.