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Improving Mindat.orgerrors in Oldoinyo Lengai pics

14th May 2018 22:36 BSTTony Peterson Expert

There are two images which purport to show reaction rims of wollastonite around elongated combeite:

They have it backward; it's rims of pseudocubic combeite over elongated wollastonite. I have uploaded a thin section image of this:

and the reaction, with probe analyses etc. is described in Contrib Mineral Petrol v 101, 458-478.

There is another image labeled gregoryite:

but this is a black, opaque mineral which is probably alabandite. There not being much to go on besides its blackness, the identification must be tentative.


19th May 2018 03:34 BSTTony Peterson Expert

Can I shine a bright light on this message again, so a manager will see it? The errors I pointed out have not been corrected. I did my Ph.D. on this occurrence and these minerals so I won't shut up till it's fixed.



19th May 2018 19:03 BSTUwe Kolitsch Manager

Message sent.

20th May 2018 02:24 BSTTony Peterson Expert

Thanks, Uwe. Two other photo captions/titles for this locale have errors that are beyond the usual typo. Perhaps the authors will see this thread……….

The usual spelling is Masai; I have never seen Messai before.

The title has Oldoinzo Lengai.

21st May 2018 19:01 BSTUwe Kolitsch Manager

Both fixed.

Interestingly, Wikipedia says Maasai:

21st May 2018 22:09 BSTJolyon Ralph Founder

Yes, Wikipedia is correct, the spelling should be Maasai, not Masai or Messai

22nd May 2018 15:20 BSTPavel Kartashov Manager

Combeite formula also is given by strange way in our database - Na2Ca2(Si6O18)0.5.

It should to be Na4Ca4[Si6O18] if we would like to give complete crystallochemical formula, or Na2Ca2Si3O9 if we want to show shortened, nonstructural its variant.

This 0.5 after anion is from area of bookkeeping, not of scientific field.

22nd May 2018 17:12 BSTUwe Kolitsch Manager

Mindat formula is now identical to IMA formula, Na4.5Ca3.5Si6O17.5(OH)0.5.

22nd May 2018 18:59 BSTPavel Kartashov Manager

I prefer hawthornian formulas of end members - or combeite end member is Na4Ca4[Si6O18], or it is Na4(Ca3Na)4[Si6O17(OH)].

22nd May 2018 23:18 BSTPavel Kartashov Manager

In other words 0.5 f.u. always is pain in ass from point of view of any classification - it is rather border between specie than real definition of species. It is very strange, that CNMNM guys don't understand this simple thing.

(Ca0.5Sr0.5)[CO3] - who it is? Or may be it should to be (Sr0.5Ca0.5)[CO3]? What it is Pd2(Sn0.5Sb0.5) - stibian paolovite, stannoan naldrettite or already another new species Pd4SnSb?

29th May 2018 22:40 BSTRalph Bottrill Manager

Both IMA and Mindat are horribly consistent in how we display formulae, if you look at the other members of the lovozerite group listed under combeite its a smambolic mixture of empirical and idealised end-member formulae, some showing H, some OH, etc. Maybe kapustinite is shown best as it clearly indicates the Si6O18 group? Probably we should show both empirical formulae and idealised end members, with structural units in brackets, to make it easier to compare related minerals. The latter style may make more sense for the IMA lists.
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