Microscope, petrographic

Maceral microscopic petrographic units of coal (ASTM D-2796 ASTM... 

Polarized-light microscope Senarmont compensator Reflected-light (metallo-graphic) microscope Petrographic slides (46x24 mm)... 

Refraction Index. Refraction index is deterrnined with a petrographic microscope by submersing a sample in emersion oils of known refractive index. 

The relation between chemistry and petrography, the science of the classification of rocks, was somewhat closer since chemical composition was thought by some petrographers to offer a basis for rational classification. But early efforts to categorize rocks by their chemical composition were frustrated as it was discovered that it was impossible to find simple chemical formulas for these bodies. Rocks of different mineral composition fell into the same chemical categories, and rocks that were chemically alike were sometimes quite different in structure, texture, and field relations. Moreover, the success of H. Clifton Sorby s technique for the microscopic study of thin sections of rocks accentuated the tendency to identify rocks on the basis of external rather than internal properties (14, 15). 

Semimicro methods of analysis have been extended to the application of such a down to earth problem as the determination of oil in wax by Wiberly and Rather (67). This procedure is certainly no academic development and is at the present time undergoing standardization in the ASTM. It will probably replace the existing macro method. These authors (68) adapted and employed analysis under the microscope to analyze sediments and deposits collected from systems employing petroleum lubricants. The petrographic and binocular microscopes are used for this purpose. 

Petrographic Studies. Polished thin sections were examined by optical methods to determine original mineralogy and alteration phases. The sections were taken and oriented in such a manner to allow comparison of the microscopic mineralogy with the results of the autoradiography experiments The shale was too fine-grained to be characterized in detail. 

The physical or petrographic components of coal are defined or described in various ways. In one system, which depends on microscopic observation, the principal components are called exinite, vitrinite, micrinite, and fusinite. Transparency of these in a thin section decreases in that order, whereas reflectance from polished surface increases in the same order. Vitrinite, the major component of most coals, occurs in bands or strands and is usually uniform in appearance, though sometimes shows cell structure exinite consists of the remains of plant spores, pollen, and cuticles with characteristic shape micrinite occurs in very fine granular form or massive structureless, irregular form fusinite shows characteristic fibrous, cellular structure. Semifusinite is transitional between vitrinite and fusinite. On a macroscopic scale, vitrain and... 

A proper understanding of the nature and behavior of resinite at all levels of rank will require considerable further effort. Petrographic examination of coals will no doubt yield additional data, but a more profitable line of attack would seem to lie in studying fresh and laboratory treated samples by a proper combination of microscopical and chemical analytical techniques. 

Briquets prepared at BCR for petrographic analysis are maintained in a desiccator for an extended period prior to microscopic analysis. Specific high moisture coals have been analyzed for reflectance at regular intervals following their insertion in the desiccating atmosphere under these conditions of continued desiccation, reflectance remained relatively constant. 

Petrographic analysis was undertaken for almost all 225 samples and an additional 100 samples from the same pottery groups. The thin section slides were examined through a petrographic polarizing microscope (Nikon Labophot-Pol and Zeiss [for photography] models were used). 

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