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Mineralogical ClassificationNovacekite (I), novacekite II and metanovacekite

20th May 2006 19:49 UTCUwe Kolitsch Manager

There appear to be some inconsistencies.


According to

Walenta, K. (1964): Rare arsenate minerals with special consideration of occurrences in the Black Forest. Mineral. Petrog. Mitt. 9, 111-174. (in German) >

novacekite I (novacekite) = Mg(UO2)2(AsO4)2.12H2O (PDF 17-147)

novacekite II = Mg(UO2)2(AsO4)2.10H2O (PDF 17-148), and

metanovacekite = Mg(UO2)2(AsO4)2.8H2O (PDF 17-152).


For novacekite, Mindat currently uses the formula Mg(UO2)2(AsO4)2.12H2O with the added comment "amount of water not confirmed".

All novacekite minerals I had X-rayed so far (from different localities) were either novacekite II or metanovacekite.

Was there any IMA decision concerning these phases?


The crystal structures of synthetic novacekite I and novacekite II were recently solved, resulting in symmetry revisions :

Novacekite I has the formula Mg(UO2)2(AsO4)2.12H2O and is triclinic, P-1, a 7.1594(5) Å, b 7.1610(5) Å, c 11.3146(7) Å, alpha 81.391(2)°, beta 81.177(1)°, gamma 88.884(1)°.

Novacekite II has the formula Mg(UO2)2(AsO4)2.12H2O and is monoclinic, P21/n, a 7.1328(11) Å, b 20.085(3) Å, c 7.1569(11) Å, beta 90.585(3)°.


The structure of natural Mg<(UO2)(As(O4)>2.4H2O was reported in 1991:

B. Bachet, C. Brassy, A. Cousson (1991) Structure of Mg<(UO2)(As(O4)>2.4H2O. Acta Crystallogr., C47, 2013-2015 (in French).

Monoclinic, space group C2/m, a = 18.207(5), b = 7.062(3), c = 6.661 (3) A, beta= 99.65(5)°.

However, it is unclear if the symmetry and water contents are correct.


I will correct the Mindat entry for novacekite, and add the refs.


Uwe Kolitsch

20th May 2006 23:12 UTCMarco E. Ciriotti Manager

The three mineral species are all with grandfathered status. So that there is no IMA decisions about them.

Marco

21st May 2006 11:31 UTCUwe Kolitsch Manager

"Novacekite II has the formula Mg(UO2)2(AsO4)2.12H2O ..."

should of course read

"Novacekite II has the formula Mg(UO2)2(AsO4)2.10H2O ..."
 
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