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Secretinite—reflectance and chemical data from two high volatile bituminous coals (Upper Carboniferous) of North America
International Journal of Coal Geology 45 Ž2001. 281–287 www.elsevier.nlrlocaterijcoalgeo
Secretinite—reflectance and chemical data from two high volatile bituminous coals žUpper Carboniferous/ of North America Paul C. Lyons a , Maria Mastalerz b,) a
b
105 Winnifred Road, Brockton, MA 02301, USA Indiana Geological SurÕey, Indiana UniÕersity, 611 North Walnut GroÕe, Bloomington, IN 47405-2208, USA Received 2 August 2000; accepted 31 October 2000
Abstract Secretinite—a maceral of the inertinite group as recognized by the ICCP in 1996—is a noncellular maceral of seed fern origin. New reflectance data indicate that this maceral has primary anisotropy with bireflectances of 0.4% to 0.9% in high-volatile B bituminous ŽRo s 0.6%. Carboniferous coal of North America. The highest reflectance is in cross-section as opposed to longitudinal section. Characteristic feature of secretinite is the virtual absence of Si and Al, unlike that in associated vitrinite. This indicates the absence of submicron aluminosilicates in secretinite and their presence in vitrinites. Secretinite is highly aromatic as indicated by low OrC ratios and high contribution of aromatic hydrogen bands detected by FTIR analysis. q 2001 Elsevier Science B.V. All rights reserved. Keywords: secretinite; inertinite macerals; Carboniferous; bituminous coal; coal chemistry
1. Introduction There has been much published discussion on the origin of the sclerotinite and its identification Že.g., Taylor and Cook, 1962.. This maceral term was introduced by Stach Ž1952. to define highly reflecting fungal remains. Subsequently, it was noticed that not all such highly reflecting bodies were of fungal origin. Therefore, it was proposed to introduce the submacerals fungo-sclerotinite ŽBenes and
) Corresponding author. Tel.: q1-604-228-2449; fax: q1-812855-2862. E-mail address: [email protected] ŽM. Mastalerz..
Kraussova, 1964; Stach, 1966., resino-sclerotinite ŽBenes and Kraussova, 1964. and secretion sclerotinite ŽICCP, 1971. to separate fungally derived sclerotinite from nonfungal bodies that were interpreted to be of resinous origin. On the basis of extensive discussion of the secretory origin of these non-fungal bodies ŽLyons et al., 1982; Thompson et al., 1983., Lyons et al. Ž1986. proposed that such constituents be recognized as a distinct maceral secretinite. This new maceral term was formally accepted by the International Committee for Coal and Organic Petrology ŽICCP. at its 48th Meeting ŽHeerlen. in 1996 ŽLyons, 2000.. At the same time, the maceral funginite was officially accepted for highly reflecting fungal remains and the maceral sclerotinite ŽStach, 1952. was abandoned.
0166-5162r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 6 - 5 1 6 2 Ž 0 0 . 0 0 0 4 1 - 0
282
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
The purpose of this paper is to summarize the physical and chemical properties of the new maceral secretinite in two high-volatile bituminous coals of North America. Included is both published information and new chemical and reflectance data.
2. Samples and techniques Samples were prepared as polished blocks using standard coal preparation techniques ŽICCP ŽInternational Committee for Coal Petrology., 1963.. Reflectance was measured using a Leitz MPV 2 microscope. Secretinite samples come from two locations: the Pomeroy coal, Holmes Mine, Appalachian Basin, West Virginia, USA ŽLyons et al., 1982.; and the St.
Rose No. 5, Evans Mine, St. Rose Coalfield, Nova Scotia, Canada ŽHacquebard, 1951.. Handpicked samples were carefully mounted in lucite, and reflectance was measured on several longitudinal sections obtained by subsequent grinding and polishing. In the case of larger rodlets of secretinite, sections were also prepared roughly perpendicular to the initial ones. On such samples, R ran , R max , and R min were determined if possible. A Cameca SX-50 electron microprobe with PAP matrix correction routine ŽPouchou and Pichoir, 1991. was used to analyze light elements ŽC and O. and S, Fe, Si, Al, Ca, and Cl. Anthracite from the Anthracite Fields of Eastern Pennsylvania, USA was used as a carbon standard and magnesite was used as an oxygen standard. Barite, fayalite, anorthite, albite, and scapolite were used as standards for the other
Fig. 1. Photomicrographs of secretinite and associated macerals, reflected light, oil immersion. ŽA. secretinite ŽSecr. rodlet Žlongitudinal section from the St. Rose No. 5 coal showing vesicles and a few kerfs, e—epoxy; ŽB. secretinite ŽSecr. in longitudinal section from the Pomeroy coal. Note kerfs and vesicles; ŽC. secretinite ŽSecr. in the coal surrounded by vitrinite ŽV. and sporinite ŽSp., cross section. Note central canal and peripheral vesicles; ŽD. secretinites ŽSecr. in cross section surrounded by vitrinite Žgray., semifusinite ŽSF. and inertodetrinite ŽI.. Scale the same as C.
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
elements. The physical conditions during analysis were as follows: an accelerating voltage of 10 kV, a beam current of 10 nA, and a beam size of 2 mm. Fourier Transform Infrared ŽFTIR. analysis was carried out on a Nicolet 710 micro-FTIR spectrometer equipped with a NICPLAN microscope. Spectra were obtained in reflectance mode at a resolution of 8 cmy1 ; 128 sample scans were co-added and ratioed to 128 scans of gold plate background. The size of a measured area was 20 mm = 20 mm. Kramers– Kronig transformation was applied to all spectra. Bands were assigned according to published sources ŽPainter et al., 1981; Wang and Griffith, 1985; among others.. The FOCAS program was used for curve deconvolution. The ratios presented in Table 3 are ratios of integration areas under the peaks and not absolute values; CH 2 and CH 3 were determined in 2800–3000 cmy1 stretching region; and aromatic bands were summed up in the 700–900 cmy1 outof-plane region.
3. Physical properties Secretinite usually occurs in subspherical or oblate-to-elongated oval forms ŽFig. 1A–D. ŽLyons et al., 1986.. In polished blocks, its shape and size depends on the rodlet section analyzed. Secretinite is noncellular and characterized by frequent kerfs Žfrac-
283
tures. and vesicles ŽFig. 1A–D.. It is a nonfluorescent and high reflectance maceral. Its reflectance is usually higher than associated semifusinite ŽLyons et al., 1986., and can be lower or higher than associated fusinite. Table 1 shows R o values and standard deviation based on 25 measurements each of secretinite, fusinite, and vitrinite. In the case of the St. Rose No. 5 coal, fusinite has considerably higher reflectance than associated secretinite, whereas in the Pomeroy coal, reflectance of secretinite is higher than that of associated fusinite. Reflectance within secretinite measured on one section is rather uniform, as expressed by low standard deviations. However, reflectance can vary substantially between individual secretinite rodlets from the same coal as well as within individual secretinite rodlets, depending upon what type of section examined Žcross, oblique, or longitudinal.. Table 2 shows reflectance data on one secretinite rodlet from the Pomeroy coal. All the reflectance measurements were collected on the same secretinite body and were taken on three cross-sections and three longitudinal sections. R max , R min , R ran and bireflectance on the cross-sections are consistently higher than on the longitudinal sections. Variation between sections of the same orientation are prominent for the cross-section Ž R max ranges from 2.1% to 3.53%. and are of much lower magnitude for the longitudinal orientation. A section parallel to the
Table 1 Reflectance and elemental composition of secretinite, fusinite, and vitrinite determined on bulk handpicked samples and with the electron microprobe technique
Microprobe analysis SR No. 5 secretinite SR No. 5 fusinite SR No. 5 vitrinite Pomeroy secretinite Pomeroy fusinite Pomeroy vitrinite
R ran Ž%.
C
O
H
N
S
Fe
Si
Al
3.24 Ž0.12. 4.68 Ž0.17. 0.6 Ž0.22. 2.8 Ž0.10. 2.2 Ž0.09. 0.6 Ž0.22.
91.7 92.1 77.2 91.3 89.4 76.4
6.42 6.29 15.1 7.61 7.89 16
nd nd nd nd nd nd
nd nd nd nd nd nd
1.34 0.99 0.71 0.18 0.64 0.78
0.02 0.05 0.01 0.01 0.01 0.01
0.005 0.03 0.28 0.005 0.87 0.25
0.00 0.02 0.21 0.00 0.70 0.14
nd nd nd
nd nd nd
Bulk analysis (dry mineral matter-free basis), data from Lyons et al. (1982) Pomeroy secretinite 2.2 Ž0.10. 81.8 12.2 3.3 0.5 0.01 nd Pomeroy fusinite 1.5 Ž0.10. 78.9 16.7 4 1.1 0.08 nd Pomeroy vitrinite 0.6 Ž0.09. 75.9 16.2 4.8 1.5 0.63 nd
Elements in weight percent. Values in parenthesis represent standard deviation. nd—no data because of N and H not determined with the electron microprobe.
Total
OrC
SrC
HrC
NrC
99.49 99.48 93.51 99.11 99.51 93.58
0.05 0.05 0.15 0.06 0.07 0.16
0.0055 0.0040 0.0034 0.0007 0.0027 0.0038
nd nd nd nd nd nd
nd nd nd nd nd nd
97.81 100.80 99.03
0.11 0.16 0.16
0.0001 0.0004 0.0031
0.49 0.61 0.76
0.005 0.012 0.017
284
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
Table 2 Reflectance of secretinite Ž R ran —random; R max —maximum; R min —minimum; Birefl.—bireflectance. measured on longitudinal and cross-sections of a secretinite rodlet of the Pomeroy coal Secretinite
Cross-section
Longitudinal section
R ran
R max
R min
Birefl.
R ran
R max
R min
Birefl.
Section 1 Std. deviation Section 2 Std. deviation Section 3 Std. deviation
1.85 0.07 2.87 0.27 3.30 0.17
2.10 0.22 3.20 0.20 3.53 0.30
1.70 0.15 2.60 0.20 2.60 0.50
0.40
1.60 0.09 1.44 0.10 1.56 0.09
1.66 0.07 1.58 0.10 1.65 0.10
1.30 0.02 1.22 0.10 1.34 0.10
0.36
0.60 0.93
0.36 0.31
Note: vitrinite reflectance of this coal is 0.6%.
long axis of the secretinite rodlet was analyzed on another rodlet from the same Pomeroy coal sample and the reflectances obtained were: R ran 1.43% Ž0.1% sd., R max 1.6% Ž0.2% sd. and R min 1.24% Ž0.1% sd.. These values are comparable to the longitudinal section from Table 2.
4. Chemical properties 4.1. Elemental composition Lyons et al. Ž1982, 1986. presented chemical data for some secretinites. Table 1 shows a subset of these data from the Pomeroy coal of West Virginia Žthe same sample site as in this study., for which elemental data are available for secretinite, fusinite, and vitrinite. In this coal, secretinite shows higher carbon content than fusinite and vitrinite, corresponding to its higher reflectance. Secretinite has lower hydrogen, nitrogen, and sulfur than either fusinite or vitrinite in the Pomeroy coal. Thus, secretinite has lower OrC, HrC, SrC, and NrC ratios as compared with the other two macerals. The other data of Lyons et al. Ž1982, 1986. show that C, H, O, N, and S of secretinite can be quite variable. The ash yield of the majority of secretinites is within the range of 3% to 6%, although secretinites of much higher ash content are also reported in the same papers. In the present study, the elemental composition of secretinite, fusinite, and vitrinite in the St. Rose No. 5 and Pomeroy coals was determined with the electron microprobe ŽTable 1.. In these coals, the carbon
content of the secretinite is 91–92%. For the St. Rose No. 5 coal, secretinite is similar in carbon content to the associated fusinite, whereas for the Pomeroy coal secretinite is higher in carbon content than fusinite, consistent with the reflectance values ŽTable 1.. Carbon content of secretinite is much higher than for the associated vitrinite, which would be expected from its more aromatic nature ŽLyons et al., 1982.. The oxygen contents of secretinite are comparable to the associated fusinite in both coals and significantly lower than for the associated vitrinite. The OrC ratio of these secretinites is much lower than for the associated vitrinites. There is a substantial difference in sulfur content between the secretinites of the two coals, the higher value occurring in the St. Rose No. 5 coal. The very low to almost undetectable Al and Si contents in the secretinite of both coals differentiate this maceral from the other two macerals. The lack of Al and Si in secretinite is consistent with the absence of submicron aluminum silicates such as illite andror kaolinite ŽLyons et al., 1987; Lyons and Hosterman, 1989.. This very pure organic nature of secretinite Žobserved also in some other Carboniferous coals. contradicts previously reported high ash content for some secretinites ŽLyons et al., 1982, 1986.. It is possible that this elevated ash content may reflect contamination. 4.2. Functional group distribution (FTIR) Lyons et al. Ž1982. showed that the FTIR spectra ŽKBr pellet technique. of secretinite were similar to those of fusinite. Both macerals have broad peaks at
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
Fig. 2. Aliphatic stretching region of secretinite and associated vitrinite in the Pomeroy coal and secretinite from the St. Rose No. 5 coal. Note intense aliphatic bands in vitrinite Ž2862, 2929 and 2964 cmy1 . and only a very broad peak in secretinites.
3400, 1600, and 1100 cmy1 , the first two assigned by the authors to residual water, and the last one to mineral matter, most likely kaolinite.
285
Fig. 4. Aromatic out-of-plane region in secretinite and associated vitrinite from the Pomeroy coal and secretinite from St. Rose No. 5 coal. Note distinct aromatic bands at 754, 812 and 872 cmy1 in secretinite; they are hardly detectable in vitrinite.
In the present study, FTIR spectra were collected using a micro-FTIR reflected mode. Even though band absorbances and peak locations by this and
Fig. 3. Stretching region after deconvolution in secretinite from the Pomeroy coal. Note aliphatic CH 2 and CH 3 bands at 2869, 2929 and 2967 cmy1 and aromatic bands at 3028 and 3066 cmy1 .
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
286
Table 3 Aromatic to aliphatic ratios ŽArrAl. and CH 2rCH 3 ratios of secretinite, vitrinite, and fusinite in the Pomeroy coal and St. Rose No. 5 coal Coal
Pomeroy coal
Maceral
Secretinite
Fusinite
Vitrinite
Secretinite
St. Rose No. 5 coal Fusinite
Vitrinite
ArrAl SD CH 2rCH 3 SD
5.0 0.1 2.1 0.2
1.9 0.1 1.8 0.2
0.7 0.1 1.1 0.1
3.3 0.1 0.5 0.1
3.0 0.1 0.9 0.1
0.7 0.1 1.1 0.1
KBr technique are similar, some differences between the spectra obtained by these two methods make comparison between them difficult ŽMastalerz and Bustin, 1995.. Reflectance micro-FTIR spectra of secretinite were generally similar to fusinite spectra, indicating the highly aromatic nature of secretinite. This aromatic nature is indicated by very low absorbances of both aliphatic stretching modes in the 2850–3000 cmy1 region ŽFig. 2. and aliphatic bending modes in the 1440–1455 cmy1 region. In the aliphatic stretching region, no distinct CH 2 or CH 3 bands could be detected in the secretinites from the Pomeroy and St. Rose No. 5 coals and their only expression is a broad peak, unlike the vitrinite from the Pomeroy coal which reveals distinct CH 2 and CH 3 peaks in this region ŽFig. 2.. However, these aliphatic bands can be detected in secretinite after deconvolution of the micro-FTIR spectra ŽFig. 3.. Aromatic hydrogen bands at 3028 and 3066 cmy1 are also distinct. The high aromaticity of secretinite is also shown by high absorbances of aromatic outof-plane bands in the 700–900 cmy1 region, with three distinct aromatic bands at 754, 812, and 872 cmy1 ŽFig. 4.. In the associated vitrinite of the Pomeroy coal, these bands are detectable but are of much lower intensity. In the secretinite of both coals, the band at 872 cmy1 is usually dominant, and is followed in intensity by those at 754 and 812 cmy1 . The dominant band in the spectra of all secretinites is an aromatic carbon band at 1595 cmy1 . The ratio of aromatic to aliphatic bands ŽArrAl. of secretinite is higher than that in fusinite for the St. Rose No. 5 coal, and is much higher than for fusinite and vitrinite in the Pomeroy coal, indicating high aromaticity of the secretinite for both of the coals studied ŽTable 3.. The CH 2rCH 3 ratio for secretinite is lower than for fusinite in the St. Rose No. 5 coal, but it is higher than that of fusinite and vitrinite
in the Pomeroy coal. The interpretation of the length of aliphatic chains or bond dissociation energy based on CH 2rCH 3 ratio is risky, however, because aliphatic bands are very weak in secretinite, often being close to background noise, which gives the CH 2rCH 3 ratio limited validity.
5. Conclusions Secretinite has variable reflectances, elemental composition, and ArrAl ratios. The reflectances ŽRr. range from 1.44% to 3.3% and ArrAl ratios from 3.3 to 5.0, both indicating a dominantly aromatic chemical structure. The reflectance and chemical data, as a whole, indicate a variable degree of aromatization within and among the secretinites analyzed. Because these variations are observed within the same coal and even the same secretinite rodlet, the cause of such variation must be related to depositional or early post-depositional causes, such as, for example, different degrees of oxidation. Secretinite in the two high volatile bituminous coals analyzed has 0.00% of Al Žwt.. and 0.005% of Si Žwt.., as opposed to 0.14 to 0.2 Žwt.%. of Al and 0.25 to 0.28 Žwt.%. of Si in the associated vitrinites, consistent with the absence of submicron aluminosilicate minerals such as kaolinite in secretinite.
Acknowledgements Cooperation and discussion with W.F. Orem ŽUSGS., F.W. Hatcher ŽOhio State University., F.W. Brown, and C.A. Palmer ŽUSGS. is greatly appreciated. Authors are also very thankful for comments and suggestions by J. Crelling, R. Wilkins, and J. Hower.
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
References Benes, K., Kraussova, J., 1964. Carboniferous fossil fungi from the Upper Silesian Basin ŽOstrava–Karvina Coal District.. Sb. Geol. Ved., Paleontol. Rada P. Svazek 4, 65–90. Hacquebard, P.A., 1951. The correlation by petrographic analyses of No. 5 Seam in the St. Rose and Chimney Corner Coalfields, Inverness County, Cape Breton Island, Nova Scotia. Geol. Surv. Can. Bull. 19, 33. ICCP, 1963. International Committee for Coal Petrology, International Handbook of Coal Petrography, 2nd edn., 1971 ŽSupplement 1., and 1975 ŽSupplement 2.. Centre National de la Recherche Scientifique, Paris, France. Lyons, P.C., 2000. Funginite and secretinite—two new macerals of the inertinite maceral group. Int. J. Coal Geol. 44, 95–98. Lyons, P.C., Hosterman, J.W., 1989. Laser microprobe ŽLAMMA 1000. chemical analysis of clay minerals; potential application to in-situ analysis of clay minerals in coal. 11th Congr. Int. Strat. Geol. Carb. ŽBeijing, 1987., C.R., vol. 5, pp. 264–272. Lyons, P.C., Finkelman, R.B., Thompson, C.L., Brown, F.W., Hatcher, P.G., 1982. Properties, origin and nomenclature of rodlets of the inertinite maceral group in coals of the central Appalachian basin, USA. Int. J. Coal Geol. 1, 313–346. Lyons, P.C., Hatcher, P.G., Brown, F.W., 1986. Secretinite: a proposed new maceral of the inertinite maceral group. Fuel 65, 1094–1098. Lyons, P.C., Hercules, D.M., Morelli, J.J., Sellers, G.A., Mattern, D., Thompson-Rizer, C.L., Brown, F.W., Millay, M.A., 1987.
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Application of laser microprobe to fingerprinting of coal constituents in bituminous coals. Int. J. Coal Geol. 7, 185–194. Mastalerz, M., Bustin, R.M., 1995. Application of reflectance micro-Fourier transform infrared spectrometry in studying coal macerals: comparison with other Fourier transform infrared techniques. Fuel 74, 536–542. Painter, P.C., Snyder, R.W., Starsinic, M., Coleman, M.M., Kuehn, D.W., Davis, A., 1981. Concerning the application of FTIR to the study of coal: a critical assessment of band assignments and the application of spectral analysis programs. Appl. Spectrosc. 35, 475–485. Pouchou, J.L., Pichoir, F., 1991. Quantitative analysis of homogenous or stratified microvolumes appluing the model APAPB. In: Heinrich, K.F.J., Newbury, D.E. ŽEds.., Electron probe Quantitation. Plenum, New York, pp. 31–75. Stach, E., 1952. Heutiger Stand des genetischen Deutung der Kohlengefugebenstandteile. 3rd Congr. Int. Strat. Geol. Carbonifere ŽHeerlen, 1951. vol. 2, pp. 585–590. Stach, E., 1966. Der Resinit und seine biochemische Inkohlung. Fortschr. Geol. Rheinld. Westfalen 13, 921–968. Taylor, G.H., Cook, A.C., 1962. Sclerotinite in coal—its petrology and classification. Geol. Mag. 99, 41–52. Thompson, C.L., Lyons, P.C., Finkelman, R.B., Brown, F.W., Hatcher, P.G., 1983. Microscopy of sclerotinites in the coal beds of the central part of the Appalachian coal field. USA J. Microsc. 132, 267–277. Wang, S.H., Griffith, P.R., 1985. Resolution enhancement of reflectance IR spectra of coals by Fourier self-deconvolution: 1. C–H stretching and bending modes. Fuel 64, 229–236.
Secretinite—reflectance and chemical data from two high volatile bituminous coals žUpper Carboniferous/ of North America Paul C. Lyons a , Maria Mastalerz b,) a
b
105 Winnifred Road, Brockton, MA 02301, USA Indiana Geological SurÕey, Indiana UniÕersity, 611 North Walnut GroÕe, Bloomington, IN 47405-2208, USA Received 2 August 2000; accepted 31 October 2000
Abstract Secretinite—a maceral of the inertinite group as recognized by the ICCP in 1996—is a noncellular maceral of seed fern origin. New reflectance data indicate that this maceral has primary anisotropy with bireflectances of 0.4% to 0.9% in high-volatile B bituminous ŽRo s 0.6%. Carboniferous coal of North America. The highest reflectance is in cross-section as opposed to longitudinal section. Characteristic feature of secretinite is the virtual absence of Si and Al, unlike that in associated vitrinite. This indicates the absence of submicron aluminosilicates in secretinite and their presence in vitrinites. Secretinite is highly aromatic as indicated by low OrC ratios and high contribution of aromatic hydrogen bands detected by FTIR analysis. q 2001 Elsevier Science B.V. All rights reserved. Keywords: secretinite; inertinite macerals; Carboniferous; bituminous coal; coal chemistry
1. Introduction There has been much published discussion on the origin of the sclerotinite and its identification Že.g., Taylor and Cook, 1962.. This maceral term was introduced by Stach Ž1952. to define highly reflecting fungal remains. Subsequently, it was noticed that not all such highly reflecting bodies were of fungal origin. Therefore, it was proposed to introduce the submacerals fungo-sclerotinite ŽBenes and
) Corresponding author. Tel.: q1-604-228-2449; fax: q1-812855-2862. E-mail address: [email protected] ŽM. Mastalerz..
Kraussova, 1964; Stach, 1966., resino-sclerotinite ŽBenes and Kraussova, 1964. and secretion sclerotinite ŽICCP, 1971. to separate fungally derived sclerotinite from nonfungal bodies that were interpreted to be of resinous origin. On the basis of extensive discussion of the secretory origin of these non-fungal bodies ŽLyons et al., 1982; Thompson et al., 1983., Lyons et al. Ž1986. proposed that such constituents be recognized as a distinct maceral secretinite. This new maceral term was formally accepted by the International Committee for Coal and Organic Petrology ŽICCP. at its 48th Meeting ŽHeerlen. in 1996 ŽLyons, 2000.. At the same time, the maceral funginite was officially accepted for highly reflecting fungal remains and the maceral sclerotinite ŽStach, 1952. was abandoned.
0166-5162r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 6 - 5 1 6 2 Ž 0 0 . 0 0 0 4 1 - 0
282
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
The purpose of this paper is to summarize the physical and chemical properties of the new maceral secretinite in two high-volatile bituminous coals of North America. Included is both published information and new chemical and reflectance data.
2. Samples and techniques Samples were prepared as polished blocks using standard coal preparation techniques ŽICCP ŽInternational Committee for Coal Petrology., 1963.. Reflectance was measured using a Leitz MPV 2 microscope. Secretinite samples come from two locations: the Pomeroy coal, Holmes Mine, Appalachian Basin, West Virginia, USA ŽLyons et al., 1982.; and the St.
Rose No. 5, Evans Mine, St. Rose Coalfield, Nova Scotia, Canada ŽHacquebard, 1951.. Handpicked samples were carefully mounted in lucite, and reflectance was measured on several longitudinal sections obtained by subsequent grinding and polishing. In the case of larger rodlets of secretinite, sections were also prepared roughly perpendicular to the initial ones. On such samples, R ran , R max , and R min were determined if possible. A Cameca SX-50 electron microprobe with PAP matrix correction routine ŽPouchou and Pichoir, 1991. was used to analyze light elements ŽC and O. and S, Fe, Si, Al, Ca, and Cl. Anthracite from the Anthracite Fields of Eastern Pennsylvania, USA was used as a carbon standard and magnesite was used as an oxygen standard. Barite, fayalite, anorthite, albite, and scapolite were used as standards for the other
Fig. 1. Photomicrographs of secretinite and associated macerals, reflected light, oil immersion. ŽA. secretinite ŽSecr. rodlet Žlongitudinal section from the St. Rose No. 5 coal showing vesicles and a few kerfs, e—epoxy; ŽB. secretinite ŽSecr. in longitudinal section from the Pomeroy coal. Note kerfs and vesicles; ŽC. secretinite ŽSecr. in the coal surrounded by vitrinite ŽV. and sporinite ŽSp., cross section. Note central canal and peripheral vesicles; ŽD. secretinites ŽSecr. in cross section surrounded by vitrinite Žgray., semifusinite ŽSF. and inertodetrinite ŽI.. Scale the same as C.
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
elements. The physical conditions during analysis were as follows: an accelerating voltage of 10 kV, a beam current of 10 nA, and a beam size of 2 mm. Fourier Transform Infrared ŽFTIR. analysis was carried out on a Nicolet 710 micro-FTIR spectrometer equipped with a NICPLAN microscope. Spectra were obtained in reflectance mode at a resolution of 8 cmy1 ; 128 sample scans were co-added and ratioed to 128 scans of gold plate background. The size of a measured area was 20 mm = 20 mm. Kramers– Kronig transformation was applied to all spectra. Bands were assigned according to published sources ŽPainter et al., 1981; Wang and Griffith, 1985; among others.. The FOCAS program was used for curve deconvolution. The ratios presented in Table 3 are ratios of integration areas under the peaks and not absolute values; CH 2 and CH 3 were determined in 2800–3000 cmy1 stretching region; and aromatic bands were summed up in the 700–900 cmy1 outof-plane region.
3. Physical properties Secretinite usually occurs in subspherical or oblate-to-elongated oval forms ŽFig. 1A–D. ŽLyons et al., 1986.. In polished blocks, its shape and size depends on the rodlet section analyzed. Secretinite is noncellular and characterized by frequent kerfs Žfrac-
283
tures. and vesicles ŽFig. 1A–D.. It is a nonfluorescent and high reflectance maceral. Its reflectance is usually higher than associated semifusinite ŽLyons et al., 1986., and can be lower or higher than associated fusinite. Table 1 shows R o values and standard deviation based on 25 measurements each of secretinite, fusinite, and vitrinite. In the case of the St. Rose No. 5 coal, fusinite has considerably higher reflectance than associated secretinite, whereas in the Pomeroy coal, reflectance of secretinite is higher than that of associated fusinite. Reflectance within secretinite measured on one section is rather uniform, as expressed by low standard deviations. However, reflectance can vary substantially between individual secretinite rodlets from the same coal as well as within individual secretinite rodlets, depending upon what type of section examined Žcross, oblique, or longitudinal.. Table 2 shows reflectance data on one secretinite rodlet from the Pomeroy coal. All the reflectance measurements were collected on the same secretinite body and were taken on three cross-sections and three longitudinal sections. R max , R min , R ran and bireflectance on the cross-sections are consistently higher than on the longitudinal sections. Variation between sections of the same orientation are prominent for the cross-section Ž R max ranges from 2.1% to 3.53%. and are of much lower magnitude for the longitudinal orientation. A section parallel to the
Table 1 Reflectance and elemental composition of secretinite, fusinite, and vitrinite determined on bulk handpicked samples and with the electron microprobe technique
Microprobe analysis SR No. 5 secretinite SR No. 5 fusinite SR No. 5 vitrinite Pomeroy secretinite Pomeroy fusinite Pomeroy vitrinite
R ran Ž%.
C
O
H
N
S
Fe
Si
Al
3.24 Ž0.12. 4.68 Ž0.17. 0.6 Ž0.22. 2.8 Ž0.10. 2.2 Ž0.09. 0.6 Ž0.22.
91.7 92.1 77.2 91.3 89.4 76.4
6.42 6.29 15.1 7.61 7.89 16
nd nd nd nd nd nd
nd nd nd nd nd nd
1.34 0.99 0.71 0.18 0.64 0.78
0.02 0.05 0.01 0.01 0.01 0.01
0.005 0.03 0.28 0.005 0.87 0.25
0.00 0.02 0.21 0.00 0.70 0.14
nd nd nd
nd nd nd
Bulk analysis (dry mineral matter-free basis), data from Lyons et al. (1982) Pomeroy secretinite 2.2 Ž0.10. 81.8 12.2 3.3 0.5 0.01 nd Pomeroy fusinite 1.5 Ž0.10. 78.9 16.7 4 1.1 0.08 nd Pomeroy vitrinite 0.6 Ž0.09. 75.9 16.2 4.8 1.5 0.63 nd
Elements in weight percent. Values in parenthesis represent standard deviation. nd—no data because of N and H not determined with the electron microprobe.
Total
OrC
SrC
HrC
NrC
99.49 99.48 93.51 99.11 99.51 93.58
0.05 0.05 0.15 0.06 0.07 0.16
0.0055 0.0040 0.0034 0.0007 0.0027 0.0038
nd nd nd nd nd nd
nd nd nd nd nd nd
97.81 100.80 99.03
0.11 0.16 0.16
0.0001 0.0004 0.0031
0.49 0.61 0.76
0.005 0.012 0.017
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P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
Table 2 Reflectance of secretinite Ž R ran —random; R max —maximum; R min —minimum; Birefl.—bireflectance. measured on longitudinal and cross-sections of a secretinite rodlet of the Pomeroy coal Secretinite
Cross-section
Longitudinal section
R ran
R max
R min
Birefl.
R ran
R max
R min
Birefl.
Section 1 Std. deviation Section 2 Std. deviation Section 3 Std. deviation
1.85 0.07 2.87 0.27 3.30 0.17
2.10 0.22 3.20 0.20 3.53 0.30
1.70 0.15 2.60 0.20 2.60 0.50
0.40
1.60 0.09 1.44 0.10 1.56 0.09
1.66 0.07 1.58 0.10 1.65 0.10
1.30 0.02 1.22 0.10 1.34 0.10
0.36
0.60 0.93
0.36 0.31
Note: vitrinite reflectance of this coal is 0.6%.
long axis of the secretinite rodlet was analyzed on another rodlet from the same Pomeroy coal sample and the reflectances obtained were: R ran 1.43% Ž0.1% sd., R max 1.6% Ž0.2% sd. and R min 1.24% Ž0.1% sd.. These values are comparable to the longitudinal section from Table 2.
4. Chemical properties 4.1. Elemental composition Lyons et al. Ž1982, 1986. presented chemical data for some secretinites. Table 1 shows a subset of these data from the Pomeroy coal of West Virginia Žthe same sample site as in this study., for which elemental data are available for secretinite, fusinite, and vitrinite. In this coal, secretinite shows higher carbon content than fusinite and vitrinite, corresponding to its higher reflectance. Secretinite has lower hydrogen, nitrogen, and sulfur than either fusinite or vitrinite in the Pomeroy coal. Thus, secretinite has lower OrC, HrC, SrC, and NrC ratios as compared with the other two macerals. The other data of Lyons et al. Ž1982, 1986. show that C, H, O, N, and S of secretinite can be quite variable. The ash yield of the majority of secretinites is within the range of 3% to 6%, although secretinites of much higher ash content are also reported in the same papers. In the present study, the elemental composition of secretinite, fusinite, and vitrinite in the St. Rose No. 5 and Pomeroy coals was determined with the electron microprobe ŽTable 1.. In these coals, the carbon
content of the secretinite is 91–92%. For the St. Rose No. 5 coal, secretinite is similar in carbon content to the associated fusinite, whereas for the Pomeroy coal secretinite is higher in carbon content than fusinite, consistent with the reflectance values ŽTable 1.. Carbon content of secretinite is much higher than for the associated vitrinite, which would be expected from its more aromatic nature ŽLyons et al., 1982.. The oxygen contents of secretinite are comparable to the associated fusinite in both coals and significantly lower than for the associated vitrinite. The OrC ratio of these secretinites is much lower than for the associated vitrinites. There is a substantial difference in sulfur content between the secretinites of the two coals, the higher value occurring in the St. Rose No. 5 coal. The very low to almost undetectable Al and Si contents in the secretinite of both coals differentiate this maceral from the other two macerals. The lack of Al and Si in secretinite is consistent with the absence of submicron aluminum silicates such as illite andror kaolinite ŽLyons et al., 1987; Lyons and Hosterman, 1989.. This very pure organic nature of secretinite Žobserved also in some other Carboniferous coals. contradicts previously reported high ash content for some secretinites ŽLyons et al., 1982, 1986.. It is possible that this elevated ash content may reflect contamination. 4.2. Functional group distribution (FTIR) Lyons et al. Ž1982. showed that the FTIR spectra ŽKBr pellet technique. of secretinite were similar to those of fusinite. Both macerals have broad peaks at
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
Fig. 2. Aliphatic stretching region of secretinite and associated vitrinite in the Pomeroy coal and secretinite from the St. Rose No. 5 coal. Note intense aliphatic bands in vitrinite Ž2862, 2929 and 2964 cmy1 . and only a very broad peak in secretinites.
3400, 1600, and 1100 cmy1 , the first two assigned by the authors to residual water, and the last one to mineral matter, most likely kaolinite.
285
Fig. 4. Aromatic out-of-plane region in secretinite and associated vitrinite from the Pomeroy coal and secretinite from St. Rose No. 5 coal. Note distinct aromatic bands at 754, 812 and 872 cmy1 in secretinite; they are hardly detectable in vitrinite.
In the present study, FTIR spectra were collected using a micro-FTIR reflected mode. Even though band absorbances and peak locations by this and
Fig. 3. Stretching region after deconvolution in secretinite from the Pomeroy coal. Note aliphatic CH 2 and CH 3 bands at 2869, 2929 and 2967 cmy1 and aromatic bands at 3028 and 3066 cmy1 .
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
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Table 3 Aromatic to aliphatic ratios ŽArrAl. and CH 2rCH 3 ratios of secretinite, vitrinite, and fusinite in the Pomeroy coal and St. Rose No. 5 coal Coal
Pomeroy coal
Maceral
Secretinite
Fusinite
Vitrinite
Secretinite
St. Rose No. 5 coal Fusinite
Vitrinite
ArrAl SD CH 2rCH 3 SD
5.0 0.1 2.1 0.2
1.9 0.1 1.8 0.2
0.7 0.1 1.1 0.1
3.3 0.1 0.5 0.1
3.0 0.1 0.9 0.1
0.7 0.1 1.1 0.1
KBr technique are similar, some differences between the spectra obtained by these two methods make comparison between them difficult ŽMastalerz and Bustin, 1995.. Reflectance micro-FTIR spectra of secretinite were generally similar to fusinite spectra, indicating the highly aromatic nature of secretinite. This aromatic nature is indicated by very low absorbances of both aliphatic stretching modes in the 2850–3000 cmy1 region ŽFig. 2. and aliphatic bending modes in the 1440–1455 cmy1 region. In the aliphatic stretching region, no distinct CH 2 or CH 3 bands could be detected in the secretinites from the Pomeroy and St. Rose No. 5 coals and their only expression is a broad peak, unlike the vitrinite from the Pomeroy coal which reveals distinct CH 2 and CH 3 peaks in this region ŽFig. 2.. However, these aliphatic bands can be detected in secretinite after deconvolution of the micro-FTIR spectra ŽFig. 3.. Aromatic hydrogen bands at 3028 and 3066 cmy1 are also distinct. The high aromaticity of secretinite is also shown by high absorbances of aromatic outof-plane bands in the 700–900 cmy1 region, with three distinct aromatic bands at 754, 812, and 872 cmy1 ŽFig. 4.. In the associated vitrinite of the Pomeroy coal, these bands are detectable but are of much lower intensity. In the secretinite of both coals, the band at 872 cmy1 is usually dominant, and is followed in intensity by those at 754 and 812 cmy1 . The dominant band in the spectra of all secretinites is an aromatic carbon band at 1595 cmy1 . The ratio of aromatic to aliphatic bands ŽArrAl. of secretinite is higher than that in fusinite for the St. Rose No. 5 coal, and is much higher than for fusinite and vitrinite in the Pomeroy coal, indicating high aromaticity of the secretinite for both of the coals studied ŽTable 3.. The CH 2rCH 3 ratio for secretinite is lower than for fusinite in the St. Rose No. 5 coal, but it is higher than that of fusinite and vitrinite
in the Pomeroy coal. The interpretation of the length of aliphatic chains or bond dissociation energy based on CH 2rCH 3 ratio is risky, however, because aliphatic bands are very weak in secretinite, often being close to background noise, which gives the CH 2rCH 3 ratio limited validity.
5. Conclusions Secretinite has variable reflectances, elemental composition, and ArrAl ratios. The reflectances ŽRr. range from 1.44% to 3.3% and ArrAl ratios from 3.3 to 5.0, both indicating a dominantly aromatic chemical structure. The reflectance and chemical data, as a whole, indicate a variable degree of aromatization within and among the secretinites analyzed. Because these variations are observed within the same coal and even the same secretinite rodlet, the cause of such variation must be related to depositional or early post-depositional causes, such as, for example, different degrees of oxidation. Secretinite in the two high volatile bituminous coals analyzed has 0.00% of Al Žwt.. and 0.005% of Si Žwt.., as opposed to 0.14 to 0.2 Žwt.%. of Al and 0.25 to 0.28 Žwt.%. of Si in the associated vitrinites, consistent with the absence of submicron aluminosilicate minerals such as kaolinite in secretinite.
Acknowledgements Cooperation and discussion with W.F. Orem ŽUSGS., F.W. Hatcher ŽOhio State University., F.W. Brown, and C.A. Palmer ŽUSGS. is greatly appreciated. Authors are also very thankful for comments and suggestions by J. Crelling, R. Wilkins, and J. Hower.
P.C. Lyons, M. Mastalerzr International Journal of Coal Geology 45 (2001) 281–287
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