Coal Petrography Laboratory

The reflectance of vitrinite remains the most definitive measure of coal rank, because, unlike volatile matter from Proximate analysis, it is unaffected by oxidation, by changes of coal type (changes in the inertinite content), or by carbonate mineral content Maceral analysis categorizes the microscopic constituents of coal according to morphology and reflectance. It is then used to determine the proportion of reactive to inert macerals for prediction of various coal quality parameters These studies are conducted using reflectance measurement by fluorescence microscope. The studies are conducted by trained geologists for In our laboratories we use polarized white halogen light, or polarized white LED light to illuminate the sample, and measure the maximum reflectance of 100 vitrinite grains in monochromatic green (546nm) light. Our reports show a histogram of the data, and lists the vitrinite types measured together with the statistics of the vitrinite distribution.


The Rank or Mean Maximum Reflectance of the Vitrinite maceral is an important measurement of the coals ability to retain or release Methane gas. Therefore, the porosity (inter-layer spacings) and absorption index of vitrinite is related to rank or reflectivity. This spread decreases as the rank increases. These intermolecular characteristics are thus valuable to coal bed methane (CBM) studies.

Coal is a complex mixture of organic and inorganic constituents (macerals and minerals, respectively). Macerals may be microscopically distinguished from one another in incident light by differences in morphology and relative reflectance. Individual macerals may be lumped into Maceral Groups, based on similarities in composition and behavior (ASTM D2796-77) as follows:

Maceral Group MaceralBehavior in Industrial Processes
Vitrinite GroupVitrinite Pseudovitrinite* Reactive
Exinite (Liptinite) GroupSporinite Resinite Cutinite Reactive
Inertinite GroupFusinite Semi-Fusinite* Micrinite Macrinite Sclerotinite Inert

Petrographic analyses are performed on representative coal samples that are crushed to minus 20 mesh, mixed with epoxy and pelletized. The coal pellets are then polished to create a planar, scratch-free surface suitable for examination in incident light (ASTM D2797-76).

The MACERAL ANALYSIS is a point- counting technique used to determine coal composition on a volume percent constituent basis (ASTM D2799-76).

The reflectance of Vitrinite particles in incident light increases with increasing rank and correlates well with rank parameters such as Volatile Matter and Carbon content. The REFLECTANCE ANALYSIS, then, may be used to indicate coal rank (ASTM D2798).

  • Maceral analysis
  • Vitrinite reflectance %
  • Cleat structure analysis