This study examines the effects of particle sizes between 3 and 121 mu m on the fundamental vibrations of the [CO32-] anion in calcite [CaCO3] as analyzed by total attenuated reflectance infrared spectroscopy (ATR-IR) and Raman spectroscopy (RS). The ATR-IR absorbance intensity ratios of the [v(4)/v(3)] [712, cm(-1)/1393 cm(-1)], [v(4)/v(2)] [712 cm(-1)/871 cm(-1)], and [v(2)/v(3)] [871 cm(-1)/1393 cm(-1)] share the same profile for grain size fractions 121 mu m through to 42 mu m mode. Between 42 and 3 mu m mode the three ratios sharply decline in a systematic manner, consistent with a nonuniform decrease in spectral contrast of the [CO32-] internal modes. Raman intensity increased with decreasing particle size from 121 mu m until 19 mu m mode particle size fraction thereafter decreasing sharply. The [v(4)/v(3)], [v(1)/v(3)], and [v(4)/v(1)] intensity ratios normalized against the corresponding intensity ratio of the 121 mu m particle size fraction indicate that the [v(4)/v(3)] ratio changes by 22%. Both ATR-IR and Raman indicate two critical points in internal mode behavior of the Raman and infrared active v(4) and v(3) internal modes, the first between 42 and 59 mu m size range and the second between 19 and 5 mu m. Results are interpreted in terms of specular to volume (diffuse) coherent transitions of internal modes and with further grain refinement internal mode specific optically thick to thin transitions.