Bernadett Bajnóczi & Mária Tóth
Institute for Geochemical Research, HAS
bajnoczi@sparc.core.hu

Cathodoluminescence (CL, electron excited fluorescence) is a visible light emitted upon the interaction between an electron beam and matter. During cathodoluminescence study some natural or artificial phases emit visible light due to excitation in samples bombarded by electrons. Excitation is caused by lattice deformations [intrinsic CL] or impurities [extrinsic CL, e.g. transition metals (Mn2+, Fe2+, etc), rare earths].

Initially cathodoluminescence was studied in natural geological materials (e.g. sandstones, limestones and marbles). CL method complements the mineralogical investigation of rock samples using petrographical study of thin sections and X-ray diffraction. Later CL has been also used on man-made materials, like pottery samples in archaeology.

CL is an efficient method to study mineral phases, different mineral paragenesis and micro- structure of minerals. Processes of mineral formation or alteration and traces of fluid migrations can be revealed, deformations and weathering in samples can be reconstructed. Together with image analysing techniques determination of quantitative distribution of mineral phases is also possible.

CL study is performed on uncovered, polished thin sections. First the texture and mineral composition of samples is determined by polarizing microscope, then thin sections or occasionally sample fragments are placed into the CL equipment.

The most frequent components of ceramics such as carbonates, quartz and feldspars, are ideal for CL study, since these minerals show luminescence of different colours and intensities. Carbonates show colours from yellow to red, quartz has blue-purple or brown luminescent colours and feldspars emit blue or greenish-yellow light.

Carbonate minerals hardly distinguishable in polarized light can be discriminated by CL, similarly the carbonate temper (rock fragments, shells) and calcareous matrix can be separated by this technique. The origin (metamorphic, magmatic and sedimentary) and the amount of aplastic inclusions can be determined. Textural and mineralogical observations allow distinguishing ceramics of different provenance and origin.