The elements of the organic material in sedimentary rock that are perceptible under incidental light are referred to as macerals. Vitrinite is the name of a group of macerals that is derived largely from terrestrial plant material.

When a sedimentary rock comes to lie deeper in the Earth?s crust during the course of geological time, the chemical composition of the organic material gradually changes under the influence of temperature, pressure and time. The oxygen and hydrogen content decreases and the carbon content increases in a process known as coalification. The degree of coalification is a measurement for the change that the organic material has undergone. By measuring the quantity of light reflected by the vitrinite, the vitrinite reflectance (VR), the degree of coalification can be determined. The higher the coalification, the higher the vitrinite reflectance.

The vitrinite reflectance measurement is performed on the collotelinite maceral. The identification of this maceral demands both knowledge and experience. Since 1998 the TNO-NITG analysts have participated in an accreditation programme of the International Committee for Coal and Organic Petrology ICCP (www.iccop.org).

Measurements

VR random mean		mean vitrinite reflectance at random orientation
VR std random mean		standard deviation of the mean vitrinite reflectance at random orientation
VR max mean		mean maximum vitrinite reflectance
VR std max mean		standard deviation of the mean maximum vitrinite reflectance
N		number of measurements

Quality
In assessing the reliability of the measurements, the possible influence that certain properties of the vitrinite may have on the measurement is fixed in a code. Three properties are assessed:

Parameter 1		VITRINITE IDENTIFICATION : coal or dispersed material, clear identification of the macerals possible
Parameter 2		PARTICLE SIZE: how well the measurement spot fits the collotelinite particle
Parameter 3		QUALITY OF THE SURFACE OF THE PARTICLES: assessment of the field of measurement (3*diam. measurement spot) in respect of scratching, minerals, relief, oxidation

Two assessments are possible:

+		may influence the measurement
0		has no influence on the measurement

Literature
ISO/DIS 7404/1: Methods for the petrographic analysis of bituminous coal and anthracite - Part 1: Glossary of terms relating to the petrographic analysis of bituminous coal and anthracite

ISO/DIS 7404/2: Methods for the petrographic analysis of bituminous coal and anthracite - Part 5: Method of determining microscopically the reflectance of vitrinite International Committee for Coal and organic Petrology (ICCP) Accreditation Exercise Methodology .

Vitrinite Classification, ICCP System 1994, International Committee for Coal and organic Petrology Aachen 1995

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