Syngenite (K 2Ca(SO 4) 2·H 2O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C s site symmetry was determined for the two sulphate groups in syngenite ( P2 1/ m), so all bands are both infrared and Raman active. The split ν 1 (two Raman+two infrared bands) was observed at 981 and 1000 cm −1. The split ν 2 (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm −1. In the infrared spectrum, only one band was observed at 439 cm −1. From the split ν 3 (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm −1. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm −1. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm −1. From the split ν 4 (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm −1. The 298 K Raman spectrum showed one band at 641 cm −1, while at 77 K four bands were observed at 607, 621, 634 and 643 cm −1. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm −1, OH-bending mode at 1631 cm −1, OH-stretching modes at 3248 (symmetric) and 3377 cm −1 (antisymmetric) and a combination band at 3510 cm −1 of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.