Geoscience Reference
In-Depth Information
S
TAINING AND ETCHING PROCEDURES
While most of the minerals present in geomaterials can
be readily identified in thin sections, some are difficult to
differentiate. These include, for example, the carbonate
minerals of limestone, gypsum and anhydrite, feldspars,
and clays in rocks. In addition, certain phases within
cement clinkers and slags require etching. Techniques
using chemical solutions or vapour selectively to etch or
stain minerals as an aid to their identification are known
to geological technicians and cement chemists. Details
of staining and etching techniques are provided in the
tables of Appendix B.
The polishing process utilizes successively finer grades of
diamond polishing compounds routinely down to 1 μm,
or even 0.25 μm for the finest work. Cementitious
materials must be dried at less than 60ºC and not exposed
to water at any stage. Thin sections may be finished by
high-polishing (called polished thin sections) and left
without cover slip to allow observation in both
transmitted and reflected light. Polished specimens are
also required for supplementary investigation using SEM.
Most highly polished specimens are usually water
sensitive and it is good practice to store them in a
desiccator, to avoid degradation from atmospheric
moisture.
