The thermal decomposition of argentojarosite has been studied by thermogravimetric, spectroscopic and infrared emission techniques. Dehydroxylation occurs in three stages at 228, 383, 463 degrees C with the loss of 2, 3 and I hydroxyl units. Loss of sulphate occurs at 548 degrees C and is associated with a loss of oxygen. At 790 degrees C loss of oxygen only leaves metallic silver and hematite. Changes in the structure of argentojarosite are also followed by the infrared emission spectra. The intensity of hydroxyl stretching vibration approaches zero by 400 degrees C confirming the loss of hydroxyl units by this temperature. At this temperature changes in the infrared spectra of the sulphate units occurs. The intensity of the sulphate stretching vibrations approaches zero by 750 degrees C. Thermal decomposition of argentojarosite is important in understanding silver production in ancient and medieval times. This work shows that temperatures of around 750 degrees C are required to produce metallic silver. (C) 2005 Elsevier B.V. All rights reserved.