Fe-57 Mossbauer spectroscopy has been used to characterize the iron-bearing minerals in the lignites from a recently discovered deposit in Giril, Rajasthan (026 degrees 03'N longitude and 071 degrees 15'N latitude). An interesting feature of these lignites is the large amount of jarosite observed which is likely to have volcanic origin. Pyrite is the other iron-bearing mineral observed. The decomposition of these minerals on combustion is studied by Mossbauer experiments on samples heated at different temperatures. The decomposition route is significantly different from those normally found in coal samples. Early rupture of the polymer matrix and repulsion of hydrogen seems to have a major role in deciding the decomposition route.