Energy Resources Program
The Organic Petrology Laboratory at the U.S. Geological Survey in Reston, Virginia, exists to produce quantitative analytical data on the organic composition and thermal maturity of coal and petroleum source rocks. This is accomplished through the petrographic examination of samples with incident light microscopes, using tungsten halogen and xenon gas discharge light sources. Organic composition of samples is determined via a point-counting examination with a mechanical stage. Thermal maturation analysis is conducted by measuring sample reflectance with a photometer and peak detection software. Textural and compositional analysis of dispersed organic material in rock samples also is accomplished through transmitted light investigations. Petrographic analyses are conducted by or under the supervision of petrographers with official accreditation from the International Committee for Coal and Organic Petrology (link to accreditation certificate examples).
Information about the organic composition and the thermal maturity of coal and petroleum source rocks can be used in a variety of applications. Maturation studies include coal rank and hydrocarbon source rock maturity assessments, which are applied in the exploration for and evaluation of energy resources.Knowledge of the organic composition of coals can be applied to predict the quality of coal resources, to improve mining strategies, and to predict coal behavior during carbonization or combustion processes. Information about the types of organic material present in petroleum source rocks is used to determine their oil- versus gas-prone hydrocarbon potential and to assess paleoenvironmental conditions of deposition.
Facilities at the Organic Petrology Laboratory include a sample preparation laboratory equipped with sample dividers, sieves, a Buehler Simplimet 3000 automatic mounting press, and a Buehler Ecomet 4 variable speed grinder-polisher. The sample preparation laboratory also contains a fume hood for preparation of larger sample blocks via epoxy resin mounts.
The microscope laboratory is equipped with an incident light Leitz Orthoplan microscope with photometer and peak detector for reflectance analysis, a Leica DMRX with mechanical stage and tungsten halogen and xenon gas discharge light sources for incident light compositional analysis, a Zeiss AxioImager equipped with tin halide illumination and a photodiode array for light detection, and a Leitz Orthoplan for examination of rock thin sections in transmitted polarized light.
The Organic Petrology Laboratory also contains a Leica M420 binocular microscope for macroscopic examination of sample mounts or larger sample blocks. A Leica DFC 480 digital camera can be mounted to each microscope for image capture. Image analysis is conducted using ImagePro Plus software routines.
Database of the United States Coal Pellet Collection of the U.S. Geological Survey Organic Petrology Laboratory
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Samples received for petrographic analyses in the U.S. Geological Survey Organic Petrology Laboratory are recorded into a log book and into a spreadsheet database. Following sample preparation and analysis, results are returned to the sample submitter via electronic transmittal. Petrographic samples are archived in cabinets and drawers in the Laboratory. Analytical data and associated electronic files (digital photographs, etc.) are retained on computer hard drives in the Laboratory and backed up onto a network server.
Samples submitted to the U.S. Geological Survey Organic Petrology Laboratory usually are prepared for analysis according to the American Society for Testing and Materials (ASTM) Standard Practice D 2797: Preparing Coal Samples for Microscopical Analysis by Reflected Light (ASTM, 2011), or the International Standards Organization (ISO) standard 7404-2: Methods for the petrographic analysis of coal-Part 2: Method of preparing coal samples (ISO, 2009).
Samples are ground to pass a 850-μm (No. 20 mesh) or 1000-μm (No. 16 mesh) sieve in most cases (as-sampled drill cuttings sometimes are mounted for reflectance analysis without grinding). The particulate sample is mounted in a 1-inch mold in a heat-setting thermoplastic powder or epoxy resin medium. Two mounts usually are made for each sample. Examination surfaces are ground and polished prior to overnight drying in a desiccator.
ASTM, 2011, Annual book of ASTM standards: Petroleum products, lubricants, and fossil fuels; Gaseous fuels; coal and coke, sec. 5, v. 5.06: ASTM International, West Conshohocken, PA, 856 p.http://www.astm.org/Standards/D2797.htm
ISO, 2009, Methods for the petrographic analysis of bituminous coal and anthracite-Part 2: Methods of preparing coal samples: International Organization for Standardization Standard 7404-2, 12 p.
Moore, T.A., and Stanton, R.W., 1985, Coal petrographic laboratory procedures and safety manual: U.S. Geological Survey Open-File Report 85-20, 68 p. http://pubs.usgs.gov/of/1985/0020/report.pdf
Pontolillo, J., and Stanton, R.W., 1994, Coal petrographic laboratory procedures and safety manual II: U.S. Geological Survey Open-File Report 94-631, 69 p. http://pubs.usgs.gov/of/1994/0631/report.pdf
Reflectance analyses are conducted according to the ASTM Standard Test Method D 2798: Microscopical Determination of the Vitrinite Reflectance of Coal (ASTM, 2008). The Laboratory uses several different standards for microscope calibration; a yttrium-aluminum-garnet (YAG) standard of 0.908% reflectance manufactured by Klein and Becker is employed for routine analyses. One hundred measurements of the maximum or random reflectance of individual vitrinite grains in the sample are performed (for coal). Fifty measurements are made on each sample mount. In some cases, as when drill cuttings samples or organically-lean materials are analyzed, there is sometimes insufficient sample present to obtain 100 measurements. There currently is no consensus standard for the measurement of the reflectance of dispersed vitrinite in petroleum source rocks; the ASTM standard referenced above (D 2798) is followed as practically as possible for this type of analysis.
Spectral fluorescence measurements are conducted according to the methods described in Baranger and others (1991) using a Zeiss AxioImager microscope system equipped with a tin halide illumination source. The light detection equipment consists of a photodiode array calibrated with the ESS Lamp described in Baranger and others (1991). There currently is no consensus standard for the measurement of the spectral fluorescence of organic materials.
The type of petrographic analysis performed is dependent on the overall design and the specific scientific goals of individual projects. Petrographic analyses usually are conducted according to the ASTM Standard Test Method D 2799: Microscopical Determination of the Maceral Composition of Coal (ASTM, 2008), or ISO standard 7404-3: Methods for the petrographic analysis of bituminous coal and anthracite-Part 3: Method of determining maceral group composition (ISO, 1994). In some cases, a modification of the ASTM D 2799 test method is included to incorporate examination with fluorescence microscopy, primarily for low-rank samples (lignite-subbituminous). For quantitative petrographic analysis, 500 identifications are performed per sample according to the ISO 7404-3 standard and 1000 identifications are performed per sample according to the ASTM D 2799 standard. When the fluorescence microscopy modification of ASTM D 2799 is incorporated into the analysis, 2000 identifications are performed per sample – 1000 under tungsten halogen illumination and 1000 under xenon gas discharge (or other ultraviolet/blue light fluorescence source, e.g., metal halide) illumination. Maceral nomenclature for huminite, vitrinite, and inertinite groups is according to the International Committee for Coal and Organic Petrology (ICCP) (ICCP, 1998, 2001; Sýkorová and others, 2005). Maceral nomenclature for the liptinite group is according to Taylor and others (1998). Mineral matter content of the sample is calculated according to the Parr Formula (ASTM, 2008) when ash yield and other pertinent data are available, and is checked against the petrographic point count.
The microscope laboratory is equipped with an incident light Leitz Orthoplan microscope with photometer and peak detector for reflectance analysis, a Leica DMRX with mechanical stage and tungsten halogen and xenon gas discharge light sources for incident light compositional analysis, and a Leitz Orthoplan for examination of rock thin sections in transmitted polarized light.
The Organic Petrology Laboratory contains a Leica M420 binocular microscope for macroscopic examination of sample mounts or larger sample blocks. A Leica DFC 480 digital camera can be mounted to each microscope for image capture. Image analysis is conducted using ImagePro Plus software routines.
ASTM, 2008, Annual book of ASTM standards: Petroleum products, lubricants, and fossil fuels; Gaseous fuels; coal and coke, sec. 5, v. 5.06: ASTM International, West Conshohocken, PA, 720 p.
Baranger, R., Martinez, L., Pittion, J., and Pouleau, J., 1991, A new calibration procedure for fluorescence measurements of sedimentary organic matter: Organic Geochemistry, v. 17, p. 467-475.
ISO, 1994, Methods for the petrographic analysis of bituminous coal and anthracite-Part 3: Method of determining maceral group composition: International Organization for Standardization Standard 7404-3, 6 p.
ICCP, 1998, The new vitrinite classification (ICCP System 1994): Fuel, v. 77, p. 349-358.
ICCP, 2001, The new inertinite classification (ICCP System 1994): Fuel, v. 80, p. 459-471.
Sýkorová, I., Pickel, W., Christanis, K., Wolf, M., Taylor, G.H., and Flores, D., 2005, Classification of huminite-ICCP System 1994: International Journal of Coal Geology, v. 62, p. 85-106.
Taylor, G.H., Teichmüller, M., Davis, A., Diessel, C.F.K., Littke, R., and Robert, P., 1998, Organic Petrology: Gerbrüder Borntraeger, Berlin, 704 p.
The U.S. Geological Survey Organic Petrology Laboratory participates in a quarterly round robin inter-laboratory exercise hosted by a commercial laboratory (CoalTech Petrographic Associates, Inc.). Results of the exercise are used to evaluate the precision and bias of our analytical methods, to develop proficiency in analyses of different sample types, to correct deficiencies in analytical techniques, and to develop evidence of the repeatability and reproducibility of analytical methods. The Organic Petrology Laboratory also participates in the round robin exercises of the relevant working groups of ICCP (e.g., Thermal Indices, Concentration of Organic Matter, Identification of Dispersed Organic Matter, and Standardization).
Petrographers in the Laboratory maintain accreditation in methods of coal and dispersed organic matter petrographic analysis from the ICCP. Accreditation information, certificate number, and expiration date are given in the footer material of individual sample reports and are available at the laboratory overview webpage.
Results of petrographic analyses of coal and rock samples in the U.S. Geological Survey Organic Petrology Laboratory usually are reported in several parts; 1) summary tables, 2) vitrinite reflectance reports, 3) petrographic reports, and 4) spectral fluorescence reports.
Summary tables encapsulate the most important numerical results of petrographic analyses of a sample suite (e.g., reflectance values) and may be prepared as Excel spreadsheet files, components of a slide presentation, or in portable document format (.pdf). The format of presentation is dependent upon the needs of the investigation.
The vitrinite reflectance report includes five components; 1) basic sample information including sample submitter, submission date, project name, sample identification, sample type, date of analysis, and the name of the analyst, 2) results, including the number of reflectance measurements, the type of organic material analyzed, the mean maximum or mean random reflectance value, the standard deviation of the mean reflectance value, and the sample rank, 3) data, including the measured reflectance values in percent to three decimal places, the maximum and minimum measured values, and the number of V-types (reflectance ranges of 0.1 percent), 4) a histogram of the reflectance data, and 5) a comment section listing pertinent details about the petrographic character of the sample.
The petrographic analysis report includes five components; 1) a header with basic sample information including sample submitter, submission date, project name, sample identification, sample type, date of analysis, the name of the analyst, the number of points counted, and the sample rank as determined by vitrinite reflectance, 2) a bar chart showing gross maceral group composition on a mineral-matter-free basis (volume percent of organic matter basis), 3) a bar chart showing organic composition on a mineral-containing basis (volume percent of whole coal/rock), 4) a data table listing the abundance of the individual organic components on mineral-containing and mineral-free bases, and 5) a comment section listing pertinent details about the petrographic character of the sample.
The spectral fluorescence report includes 1) basic sample information, 2) results, including mean spectral parameters λmax, Q650/500, Qmax/500, Hw, and Rh (see Bustin and others, 1985), 3) an example photograph of the analyzed material, 4) spectral signatures and a calculated mean spectrum, 5) raw data measurements, and 6) a comment section for the analyst to provide sample documentation.
Bustin, R.M., Cameron, A.R., Grieve, D.A., and Kalkreuth, W.D., 1985, Coal petrology: its principles, methods, and applications: Short Course Notes, Geological Association of Canada, v. 3, 229 p.
Page Last Modified: Tuesday, June 09, 2015