PSICAT is a very nice tool to create lithology logs for sediment cores. One of the most interesting features of PSICAT is it's own XML export format. The format is very simple, it basically consists of two element: 'model' and 'property'. 'Model' is just a simple container for data and can represent an Interval, Bed or Lithology etc.. A 'model' can contain several 'property' elements, which represent simple key value pairs. Here is an example:
UPDATE: The code and tool has been moved, please visit http://www.lithologs.net !