The chemical composition of pyrite in coal can be used to investigate its geological and mineralogical origin. In this paper, high-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to study the chemical composition Of various pyrite forms in the No.9 coal seam (S(t,d) = 3.46%) from the Wuda Coalfield, Inner Mongolia, northern China. These include bacteriogenic, framboidal, massive, cell-filling, fracture-filling, and nodular pyrites. In addition to Fe(+) ((54)Fe(+), (56)Fe(+), (57)Fe(+)), other fragment ions were detected in bacteriogenic pyrites, such as (27)Al(+), Si(+) ((28)Si(+), (29)Si(+), (30)Si(+)), (40)Ca(+), Cu(+) ((63)Cu(+), (65)Cu(+)), Zn(+)((64)Zn(+), (66)Zn(+), (67)Zn(+), (68)Zn(+)), Ni(+) ((58)Ni(+), (60)Ni(+), (62)Ni(+)), and C(3)H(7)(+). TOF-SIMS images show bacteriogenic pyrites are relatively rich in Cu, Zn, and Ni, suggesting that bacteria probably play an important role in the enrichment of Cu, Zn, and Ni during their formation. Intense positive secondary ion fragments from framboidal aggregates, such as (27)Al(+), (28)Si(+), (29)Si(+), AlO(+), CH(2)(+), C(3)H(3)(+), C(3)H(5)(+), and C(4)H(7)(+), indicate that formation of the framboidal aggregates may have occurred together with clay mineral and organic matter, which probably serve as the binding substance. The intense ions of (28)Si(+) and (27)Al(+) from massive pyrites also suggest that their pores incorporated clay minerals during crystallization. Together with the lowest (28)Si(+)/(23)Na(+) value, the intense organic positive secondary ion peaks from cell-filling pyrites, such as C(3)H(3)(+), C(3)H(5)(+), C(3)H(7)(+), and C(4)H(7)(+), indicate 5 7 7 that pyrite formation may have accompanied dissolution or disintegration of the cell. The intense P(+) peak was observed only in the fracture-filling pyrite and the highest (28)Si(+)/(23)Na(+) value of fracture-filling pyrite reflects its epigenetic origin. Together with XRD and REEs data, the stronger (40)Ca(+) in nodular pyrite than other pyrite forms shows seawater influence during its formation. (C) 2003 Elsevier B.V. All rights reserved.