Dear Xander,
to add to what Dave just said.
Your black 'needles', which appear prominently in your samples 3 and 4, are
certainly negatives of a crystal phase which in the meantime has weathered
away selectively. In sample 4 you can see some remaining, medium grey,
material in the otherwise black voids. I have seen similar things in a
number of sections, typically related to vitrified siliceous materials
(glass related in this case). The star-like crystals in sample 2 could
probably be some alumina-rich spinel; I would be surprised if they were
wuestite.
Otherwise, I totally agree with Dave that you need to either thin-section
these, or SEM / microprobe them to identify the non-opaque phases properly.
Thilo
******************************************
Thilo Rehren
Professor of Archaeological Materials and Technologies
Institute of Archaeology
University College London
31-34 Gordon Square
London WC1H 0PY
Great Britain
(44) 20 7679 4757
(44) 20 7383 2572 fax
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