Natural coke

L. Schmidt, A. B. Ford, and Robert D. Brown of the U.S. Geological Survey collected a float specimen of natural coke at Aztec Nunatak in the Pensacola Mountains to complete the list of coal localities now known along the Trans-antarctic Mountains. 

Coal Petrography. Of the 36 samples examined microscopically, approximately one-half contained gas vacuoles produced by thermal distillation of the coal. Thus, these coals that might otherwise have been referred to the rank of anthracite can be regarded as natural coke. All the samples, including those with gas vesicles, appeared to be fairly dense, with no macroscopic indication of a coke-structure development. The samples with the most advanced vacuole development appeared to be almost metallic in luster. All the coal entities normally encountered—vitrinoids, micrinoids, semifusinoids, and fusinoids— were present, whereas the exinoids and resinoids, which are difficult to identify with certainty in semianthracite or anthracite, were not positively identified in... 

Figure 3. Examples of the Mi-crostructural variations that accompany the transition from natural coke to coal. The photomicrographs are arranged in sequence of increasing distance below the intrusive (sill) that was the source of heat reflected light X 255...

Large vacuole (black) surrounded by coke wall (gray). This natural coke appears 132 feet below a 600-F diabase sill... 

Figure 4. The appearance of natural coke that occurs in the Antarctic coal measures reflected light X 150...

Hardness. The Antarctic coals have Knoop hardnesses that range from 27 kg./sq. mm. to 188.6 kg./sq. cm. (Table I). Other natural cokes are generally the hardest, and the semianthracites are generally the softest. Hardness increases as the distance from the sill decreases for the coals from the Terrace Ridge area (Figure 11). However, when all the samples are considered, the hardness does not necessarily correlate in a completely regular manner with another single set of test data. 

Two general areao in Colorado exhibit extensive alteration of coalo by igneouo intrusives. The first locality it near Somerset in the west central part of the state, and the second area is the Spanish Peaks region near Trinidad and Walsenburg. Drill core samples, outcrop samples, materials from active mines, and thin sections of the intrusive rocks were studied. The results show that mean maximum reflectance of the altered coal or natural coke increases as the distance from an intrusive body decreases. Carbon and ash values increase as the distance from intrusive decreases whereas volatile matter values decrease. Sulfur data are variable. Hydrogen values increase as the distance from an intrusive increases. Hydrogen and reflectance are considered the most sensitive and reliable indicators of degree of alteration. 

Two diamond drill cores, designated DDH-A and DDH-B were obtained from central Colorado. DDH-B is from the vicinity of Redstone, Gunnison County, and core DDH-A is from the vicinity of Somerset in Delta County. These samples were particularly interesting since there is a transition from unaltered high volatile bituminous coal to natural coke at the igneous contacts. Both cores are of Cretaceous age coal. All core samples are from depths in excess of 1500 feet below the surface. 

Figure 5. Photographs of thin sections from core DDH-A showing some of the features along contact zone of the sill and natural coke.

Exposures in the Black Beauty mine, near the surface in the main slope, show normal unaltered coal of a high volatile C rank. That this has most probably been affected by the intrusion of the dike is evidenced by high concentrations of spheroidal coal or coal apples. Johnson (JO) has reported on spheroidal coal and concluded that development of these structures is related in this area to the igneous intrusions. Further into this mine the entire seam becomes altered to natural coke in rooms headed toward the dike. In these areas mining had to be terminated for this reason. Large areas are exposed,... 

Natural Coke at Sopris. At Sopris Colo., approximately four and one-half miles west of Trinidad, on Colorado State Highway 12, there are some striking exposures of a basaltic sill which has completely altered a coal seam and in some areas almost entirely replaced it. The natural coking process has been so extensive in this area that attempts were made years ago to actually mine coke. Figure 7 shows an exposure at Sopris where the sill material has invaded the coal seam in several layers. The lighter, more massive beds are the... 

Figure 7. Natural coke and basaltic sill at Sopris locality. Silver dollart for scale, rests against band of well- fingered natural coke. A band of the sill is lighter material beneath...

Figure 8. Coal seam highly altered hy basaltic sill at Sopris locality. Large conduit-like mass of sill rock in center with natural coke surrounding. Coke arches up and over the conduit-like mass. Seam is underlain by black shale and capped with a thin black shale and a massive light gray sandstone...

Figure 9. Natural coke xenolith in sill, one-half mile east of Medina Plaza. Sill has replaced most of the coal seam in this area. The letters A and B in the photograph indicate the longest dimension of the xenolith. It is approximately 9 x/z feet between these stations...

Figure 10. Carbon and volatile matter distribution across xenolith of natural coke...

In addition to reflectance measurements, the pellets were studied microscopically employing a gypsum plate. This is one of the most effective ways of observing coke differences without relying on mechanical measurements. The appearance of the various constituents of the coke, whether flat, mottled or striated and the degree of anisotropy readily indicated the type of coal from which the coke is produced (1). Utilizing the gypsum plate, microscopically this natural coke appeared striated and anisotropic. Production coke from a low volatile coal has this same appearance. 

The coal bed from which this natural coke was formed has not been traced to an unaltered area. However, data reported previously indicated that the coal seams of this general area are in the high volatile range. This discrepancy between the reported volatility and the character of the coal particles in the coke may be a result of a relatively rapid increase in the stage of metamorphism immediately prior to coking of the coal by the heat from the igneous intrusion. 

Natural, coke-oven, and refinery gas Register-type burners 5-10... 

Khorasani G. K., Murchison D. G. and Raymond A. C. (1990) Molecular disordering in natural cokes approaching dyke and sill contact. Fuel 69, 1037—1046. 

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