Figure 2. A typical IR spectrogram of the three most common gallbladder stone types.

A. Cholesterol stone: 1466, 1377, and 1057 cm⁻¹ were the characteristic absorption peaks of cholesterol. B. Pigment stone: 1663, 1629, 1570, and 1247 cm⁻¹ were the characteristic absorption peaks of bilirubin and bilirubinate. C. Calcium carbonate of calcite type: 1436, 875, and 712 cm⁻¹ were the characteristic absorption peaks of calcium carbonate of calcite type. D. Calcium carbonate of aragonite type: 1494, 854, 713, and 700 cm⁻¹ were the characteristic absorption peaks of calcium carbonate of aragonite type.