Tucekite
(3rd world occurrence)
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Tucekite (Ni9Sb2S8)
is an
extremely rare mineral in global
terms. It is a nickel antimony
sulphide, and belongs to the
hauchecornite group of minerals.
The only other occurrences of
tucekite so far described are the
type ones, namely Kanowa, Western
Australia (from a mineralised
Archaean chlorite schist) and the
Witwatersrand, South Africa,
where it has been identified in
sulphide-bearing concentrates
from two mines. And here it is,
in Central Wales, in hydrothermal
veins!
I first noticed this mineral in
the mid 1980s in several polished
sections from mines to the east
of Talybont: Eaglebrook, Henfwlch
(these shots), Esgairhir,
Esgairfraith and Hyddgen. It was
widespread and unidentified, all
the more perplexing because of
its tendency to form highly
distinctive euhedral tetragonal
crystals. A combination of
microprobe and XRD analysis with
the assistance of Dr David Bland
and Mr Peter Nancarrow at BGS
finally sorted it out two years
later. Why such a globally rare
mineral is present in this tight
cluster of localities, in
quantity, remains to be answered.
Tucekite is not that impressive
in plane polarised light, but
just cross your polars and have
another look - it is then one of
the most colourful ore minerals
in existence as you will see by
clicking HERE. Crystals
range in size up to about 0.5mm
or so. Associated species are
galena, chalcopyrite, ullmannite,
pyrite, electrum, siegenite and
millerite.
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