In order to obtain an estimate of the maximum piezoelectric polarization possible for alpha quartz, the principal piezoelectric coefficient is calculated on the basis of a hard‐sphere, rigid‐ion model. The result, obtained by purely geometrical reasoning (including anad hocgeometrical constraint), fits the measured value ofe11with an ``effective ionic charge'' of one‐sixth the free ionic charge. Extension of the calculation to finite compressive strain yields a maximum polarization of 3.4 &mgr;coul/cm2at a 34% strain. (Compare withe11=16.7 &mgr;coul/cm2per unit strain.) For higher strains the polarization drops off rapidly, but the model becomes inconsistent for strains greater than 43%. A test for more general validity of the model, by obtaining directly the ratio of the two independent piezoelectric coefficients,e14/e11, yields seven times the measured ratio.