Phase-change rule coordinate properties

The changes in volume, electrical conductivity, and optical properties that accompany these polymorphic transitions of silica are discussed by Eitel [1952], who also critically reviews the influence of such features as heat pretreatment, pressure, and contaminants on the characteristics of these inversions. The polymorphic transitions of silica may be very slow or may occur without appreciable evidence of inhibition. An empirical rule that crystal phases with lower coordination numbers are more stable at high temperatures than those with higher coordination numbers was postulated by Goldschmidt [1926]. 

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