Simplified petrographic description
Mineralogical characterization: Simplified petrographic description
Teemu Karlsson, Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND, e-mail: teemu.karlsson(at)gtk.fi
Petrography focuses on microscopic description of stone materials. A petrographic description of rocks is important not only for the purposes of classification of rock type but also in order to investigate constituents, textures and other features influencing its chemical, physical and mechanical behaviour, which affect the measures needed for the proper waste facility closure.
Here the simplified petrographic description made according to the European Standard EN 932-3:1996 with the incorporation of its amendment A1:2003 is evaluated. The method is commonly used e.g. at the Geological Survey of Finland. The standard covers only natural stone material, like natural originated crushed aggregates or the original rock material, sand and gravel.
Figure 1. Thin sections of mica gneiss rock samples on a transmitted light microscope; Biotite is shown as brown, quartz and plagioclase as white and sulphides as black opaque. A thin section investigation with a petrographic microscope is an essential part of the simplified petrographic description. Photo: GTK
Description of the method
The method includes a macroscopic description of a hand specimen and a more detailed investigation of a thin section with a petrographic microscope i.e. transmitted light microscopy or reflected light microscopy (Fig. 1). If the sample contains opaque minerals such as oxides and sulphides, polished thin sections and reflected light (ore microscopy) is used. The mineral abundances are determined by a standard point-counting method (600 points), where the general grain size and the occurrence of opaque minerals make it possible. The rock type is classified according to recommendable nomenclature.
More detailed information about the EN 932-3:1996/A1:2003 standard can be enquired from the European Committee for Standardization.
The method can be used to characterize natural stone material, like crushed aggregates or the original rock material, sand and gravel. The mineral contents and species’ of the rocks can be determined, which is crucial when assessing the waste materials potential to produce acid mine drainage. Based on results the longer term environmental behaviour of the waste rock material can be estimated.
- relatively cheap, widely used and established, many proven and documented applications.
- depends on the skills of the investigator (should be a geologist specialized in microscopy),
- results are primarily valid for the studied thin section and do not necessarily stand for other thin sections or samples taken from the same source,
- hard to detect small amounts of accessory minerals.
Finnish Standard Association (SFS) 2003. Tests for aggregates, SFS Handbook 157.
European Committee for Standardization (CEN) 1996/2003, EN 932-3:1996/A1:2003, Tests for general properties of aggregates – Part 3: Procedure and terminology for simplified petrographic description.