Origin :
Rapid Creek, Yukon, Canada
History :
Obtained as a gormanite specimen for structure determination purpose.
But the gormanite crystals are systematically twinned so that the structure
determination was attempted from powder data, and was successful (to be
published). The sample is not pure gormanite, and even the final synchrotron
powder pattern Rietveld fit was greatly improved by taking account of three
impurities (1-3% for each of them). The identification of these 3 impurities
was made by using a search-match program on a powder pattern recorded from
a part of the sample containing as few gormanite as possible. This is that
pattern which was selected for the SMRR.
Problems on the pattern :
The sample-1 pattern presents a zeroshif which does not preclude identification.
Anyway, it can be detected easily from the shift of the hkl lines
of obvious phases like quartz or siderite or hydroxylapatite. We decided
to not correct the pattern from the zeropoint error, in order to increase
the difficulty level. Anyway, many identifications by a search-match program
are made from a routine pattern, with a sample deposited on a glass sample
holder so that the sample is frequently above the diffracting plane (the
glass sample holder surface being exactly in the diffracting plane).
Notes :
Gormanite and souzalite belong to the same series, so that souzalite
is also a correct answer.
It is not impossible that the proposals of some of the SMRR participants
for other minor phases in sample 1 are true (alluaudite, etc). But this
would be hard to prove due to the very small contribution to the pattern.