1) Fluctuation 2) Variation 
Allomerism is the similarity in the crystalline structure of substances of different chemical composition. ...
• (n.) Variability in chemical constitution without variation in crystalline form.
Al·lom'er·ism noun [ Greek ... other + ... part.] (Chemistry) Variability in chemical constitution without variation in crystalline form. 
Type: Term Pronunciation: ă-lom′er-izm Definitions: 1. The state of differing in chemical composition but having the same crystalline form.
[n] - (chemistry) variability in chemical composition without variation in crystalline form
allomerism, allomerize, allomer Substances with a different chemical composition but the same crystalline form.
noun (chemistry) variability in chemical composition without variation in crystalline form
variability in chemical constitution without change in crystalline form.