The onset conditions for ice nucleation on H₂SO₄ coated, (NH₄)₂SO₄ coated, and uncoated kaolinite particles at temperatures ranging from 233 to 246 K were studied. We define the onset conditions as the relative humidity and temperature at which the first ice nucleation event was observed. Uncoated particles were excellent ice nuclei; the onset relative humidity with respect to ice (RH_i) was below 110% at all temperatures studied, consistent with previous measurements. H₂SO₄ coatings, however, drastically altered the ice nucleating ability of kaolinite particles, increasing the RH_i required for ice nucleation by approximately 30%, similar to the recent measurements by Möhler et al. [2008b]. (NH₄)₂SO₄ coated particles were poor ice nuclei at 245 K, but effective ice nuclei at 236 K. The differences between H₂SO₄ and (NH₄)₂SO₄ coatings may be explained by the deliquescence and efflorescence properties of (NH₄)₂SO₄. These results support the idea that emissions of SO₂ and NH₃ may influence the ice nucleating properties of mineral dust particles.