Xander-
I had a look at the images of slags/vitrified clays posted at
> http://huizen.dds.nl/~trenador
>
I have a great deal of experience with examination of these types of material
in standard polished thin (30 micron) thin sections in both transmitted and
reflected light. Your pictures are all taken in reflected light, which limits
what I can say about them. It would be much more useful if you had three
images of the same field of view (transmitted plane polarized light,
transmitted cross-polarized light and reflected light, preferably with the
first two in colour).
I am quite certain that the grey laths in the center of the field from HA 97 46
are mullite (Al6Si2O13; orthorhombic).I don't know what the star-like
crystallites in HA 97 47 are, but they are certainly not clay minerals! From
their reflectance, they are probably silicates of some kind, but electron
microprobe analysis (EPMA) or X-Ray Diffraction would be needed to identify
them. The black crystals in HA 97 51 and HA 97 54 are interesting, since very
few minerals have such low reflectance. I have not come across anything
similar. From their appearance these ARE crystals, not "burnt-out" plant fibres
as you suggest. EPMA and examination in transmitted light in thin section are
needed. The grey mineral forming polygonal crystals in HA 97 55 is not
identifiable in reflected light - very few silicate minerals are. You don't
give a bulk composition for this one, but it would appear (from the presence of
iron oxide dendrites) to have much higher iron content than the other
specimens. If this is so, the grey laths are probably olivines (fayalite,
kirschteinite) or pyroxenes. Again, you need transmitted light tin section
study and/or EPMA.
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