Primary nucleation of burkeite, which is a crystalline solid solution of sodium carbonate and sodium sulfate having the stoichiometry Na2CO3.2Na(2)SO(4), was monitored using an on-line particle-size analyzer. Observations of unusual nucleation behavior led to explorations that identified specific impurities in the system that affected nucleus formation. By varying the conditions under which nucleation occurred, calcium ions were found to inhibit nucleation, and further research showed that the substitution of calcium ions into the burkeite crystal lattice was the reason for the observed behavior.