WVGESTrace Minerals in West Virginia Coals

Click Here To Go To Trace Elements Framed Home Page Chalcopyrite: Copper iron disulfide (CuFeS2)

Chalcopyrite, like pyrite, formed within the peat early in the coal's history.  Chalcopyrite crystals could form anywhere within the peat, but often preferentially grew within open voids such as in semifusinite ("fossil charcoal") SEM photomicrograph showing chalcopyrite, galena, sphalerite and kaolinite filling voids in semifusinitealong with other sulfide minerals.  In semifusinite, the original plant cell walls were carbonized by fire into strong, pure carbon, remnants of the original cell walls with openings where the cell contents were located.  Dissolved ions in the peat waters precipitated into various minerals in these voids as the peat formed.  In this SEM photomicrograph of the Stockton coal from Boone County WV, kaolinite, chalcopyrite, galena and sphalerite fill cavities in semifusinite.  Chalcopyrite and galena both grew within a single 30 µm opening (dots at the bottom of the photograph are each 10 µm apart).  Silicon and aluminum were most abundant and crystallized into very common kaolinite, Al4(Si4O10)(OH)8, iron, sulfur and copper formed less common chalcopyrite, zinc and sulfur formed sphalerite, ZnS, and lead and sulfur formed galena, PbS. In this study, copper statistically correlated only with lead, suggesting that this relationship between chalcopyrite and galena may be somewhat widespread in West Virginia coals.  Chalcopyrite was observed in moderate amounts in 18 of 24 coal samples examined with the SEM in an unpublished study by the WVGES.
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