Redefinition of satimolite

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Marco E. Ciriotti
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Redefinition of satimolite

Messaggio da Marco E. Ciriotti » lun 27 nov, 2017 8:27

Referenza:
▪ Pekov, I.V., Zubkova, N.V., Ksenofontov, D.A., Chukanov, N.V., Yapaskurt, V.O., Korotchenkova, O.V., Chaikovskiy, I.I., Bocharov, V.M., Britvin, S.N., Pushcharovsky, D.Yu. (2018): Redefinition of satimolite. Mineralogical Magazine, 82, (in press).

Abstract:
The borate mineral satimolite, which was first described in 1969 and remained poorly-studied until now, has been re-investigated (electron microprobe analysis, single-crystal and powder X-ray diffraction studies, crystal structure determination, IR spectroscopy) and redefined based on the novel data obtained for the holotype material from the Satimola salt dome and a recently found sample from the Chelkar salt dome, both in North Caspian Region, Western Kazakhstan. The revised idealized formula of satimolite is KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O (Z = 3). The mineral is trigonal, space group R-3m, unit-cell parameters: a = 15.1431(8), c = 14.4558(14) Å, and V = 2870.8(4) Å3 (Satimola) and a = 15.1406(4), c = 14.3794(9) Å, and V = 2854.7(2) Å3 (Chelkar). The crystal system and unit-cell parameters are quite different from those reported previously. The crystal structure of the sample from Chelkar was solved based on single-crystal data (direct methods, R = 0.0814) and the structure of the holotype from Satimola was refined on a powder sample by the Rietveld method (Rp = 0.0563, wp = 0.0761, Rall = 0.0667). The structure of satimolite is unique for minerals. It contains twelve-membered borate rings [B12O18(OH)12] in which BO3 triangles alternate with BO2(OH)2 tetrahedra sharing common vertices, and octahedral clusters [Me7O6(OH)18] with Me = Al5Mg2 in the ideal case, with sharing of corners between rings and clusters to form a three-dimensional heteropolyhedral framework. Each borate ring is connected with six octahedral clusters: three under the ring and three over the ring. Large ellipsoidal cages in the framework host Na and K cations, Cl anions and H2O molecules.

NdR1: Poichè Mg è un elemento essenziale della specie la ridefinizione avrebbe dovuto essere prioritariamente approvata dall'IMA CNMMC.
"Mg2+ is not a predominant constituent in the Al sites but it is an important charge-compensating cation that makes necessary to include Mg in the idealized formula of satimolite".

NdR2: I seguenti borati hanno tutti lo stesso (l.s.) tipo (FBB) di struttura (dodecaborati): il blocco fondamentale è infatti formato da 12 unità: triangoli e tetraedri. Interessante notare che in tutti è presente il Cl.
Brianroulstonite Ca3[B5O6(OH)6]Cl2(OH)·8H2O
Penobsquisite Ca2Fe2+[B9O13(OH)6]Cl·4H2O
Pringleite Ca9[B26O34(OH)24Cl4]·13H2O
Ruitenbergite Ca9[B26O34(OH)24Cl4]·13H2O
Satimolite KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O

NB: Pringleite e ruitenbergite sono polimorfi.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
Messaggi: 24842
Iscritto il: ven 25 giu, 2004 11:31
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Re: Redefinition of satimolite

Messaggio da Marco E. Ciriotti » ven 09 nov, 2018 20:59

Pubblicazione effettuata.

Referenza:
▪ Pekov, I.V., Zubkova, N.V., Ksenofontov, D.A., Chukanov, N.V., Yapaskurt, V.O., Korotchenkova, O.V., Chaikovskiy, I.I., Bocharov, V.M., Britvin, S.N., Pushcharovsky, D.Yu. (2018): Redefinition of satimolite. Mineralogical Magazine, 82, 1033-1047.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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