Applications of Ore Microscopy to Coal Petrography



Coal petrography uses reflected light microscopy on polished sections of coal to identify the coal macerals (like minerals, but with variable compositions) and assess the cokability of various coals. Vitrinite (V, dark gray; banded) and pseudovitrinite (Pv, lighter gray, no banding) particles in Herron No. 5 coal, Illinois. The coal macerals are embedded in plastic. Reflected light, medium magnification (200X in original slide).



Another photomicrograph showing the application of reflected light microscopy to the study of coals. Although coal macerals are much darker than ore minerals, the contrast in brightness (reflectance) is sufficient to readily distinguish the coal constituents. For example, although fusinite (F; white) has a reflectance (R) of only 3 (3% of the light is reflected by fusinite), it is easily distinguished from pseudovitrinite (Pv; gray) particles with a R=1%. Vitrinite shows banding and has a R of 1%, part of the banding is due to the inclusions of spores (sporinite; S). All of the maceral particles are embedded in a plastic. Herron No. 5 coal, Illinois, medium magnification (200X in original slide).

Applications of Ore Microscopy to Exploration



Potassic fenitization of host rock in association with a carbonatite intrusion. Trace ferrous iron in the original potash feldspar (blue) has been oxidized to ferric iron by the oxidizing character of the fluids associated with the carbonatite, and the ferric iron serves as an activator for red cathodoluminence (CL) in the potassic feldspar. The change from blue to red CL in feldspar has been used as an indication of the presence of carbonatite intrusions and associated ore deposits. Carbonatitic calcite (yellow) also has been introduced into the fenite. Quartz cathodoluminesces dull reddish brown. Fen, Norway. Cathodoluminence microscopy, moderate magnification.