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Improving Mindat.orgOdd siegenite

24th Mar 2017 11:44 UTCReiner Mielke Expert

https://www.mindat.org/photo-9755.html so why is this siegenite? Why not pyrrhotite?

24th Mar 2017 12:26 UTCDavid Von Bargen Manager

If you look at the detailed locality page "Siegenite, dolomite and dickite confirmed by XRD at the National Museum of Wales"

24th Mar 2017 12:44 UTCFrank Keutsch Expert

I have a specimen that has "hexagonal" platy siegenite, which is also analyzed. I had assumed that they were spinel law twins...

Frank

24th Mar 2017 13:20 UTCTom Cotterell

There have always been queries surrounding these 'hexagonal' platy crystals. The silvery-grey octahedral crystals are siegenite and have been chemically analysed from other localities in the South Wales Coalfield. However, I am not certain that the platy crystals have been analysed either chemically, or structurally. I have checked through the XRD records available at the National Museum of Wales and the only analysis of material from Gelli Colliery unhelpfully provides no description of the shape of the crystal - which was identified, using X-ray film in 1992, as near to violarite (structurally very similar to siegenite which I am confident it would prove to be if analysed chemically). A little more information is available at https://museum.wales/mineralogy-of-wales/database/?mineral=95 .

Tom

Amgueddfa Cymru - National Museum Wales

24th Mar 2017 13:23 UTCErik Vercammen Expert

Malformed, flattened octahedrons can mimic hexagonal plates.

24th Mar 2017 13:39 UTCReiner Mielke Expert

I am aware that isometric crystals can mimic hexagonal ones, but if you are going to claim you have the largest "hexagonal" crystal known then it would seem to me you should have to prove it with analysis. Furthermore I see no reason why you could not have pyrrhotite associated with siegenite.

24th Mar 2017 16:27 UTCAlfredo Petrov Manager

I'm not sure whether siegenite has any magnetism? If not, then one could easily distinguish it from pyrrhotite with a tiny magnet.

24th Mar 2017 17:24 UTCIan Jones Expert

Reiner Mielke Wrote:

-------------------------------------------------------

> https://www.mindat.org/photo-9755.html so why is

> this siegenite? Why not pyrrhotite?

As it's my specimen, perhaps you should have asked me.

This was covered some years ago https://www.mindat.org/forum.php?read,7,161834,162281#msg-162281. The crystals analysed at the NMW from Gelli were "hexagonal" crystals and were also from me. Also ID'ed at the same time were "hexagonal" crystals from elsewhere in the coalfield collected by, and then visually identified as pyrrhotite in Naylor Firth's PhD thesis, and held in the NMW collection. All were identified as siegenite.

24th Mar 2017 17:44 UTCReiner Mielke Expert

Right. Sorry about that I should have checked the past discussions.

24th Mar 2017 17:48 UTCReiner Mielke Expert

Hello Ian,

Could you or someone else be so kind as to put a link to that earlier discussion in the description of the sample?

26th Mar 2017 18:06 UTCIan Jones Expert

Have done that

27th Mar 2017 01:12 UTCReiner Mielke Expert

Thank you Ian!

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