IMA 2018-048 = bicapite

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Marco E. Ciriotti
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IMA 2018-048 = bicapite

Messaggio da Marco E. Ciriotti » mer 18 set, 2019 19:54

Prossima pubblicazione.

Referenza:
▪ Kampf, A.R., Hughes, J.M., Nash, B.P., Marty, J. (2019): Bicapite, KNa2Mg2(H2PV5+14O42)·25H2O, a new polyoxometalate mineral with a bicapped Keggin anion from the Pickett Corral mine, Montrose County, Colorado, U.S.A. American Mineralogist, 104, (in press).
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: 26171
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: IMA 2018-048 = bicapite

Messaggio da Marco E. Ciriotti » mar 03 dic, 2019 18:02

Pubblicazione effettuata.

Referenza:
▪ Kampf, A.R., Hughes, J.M., Nash, B.P., Marty, J. (2019): Bicapite, KNa2Mg2(H2PV5+14O42)·25H2O, a new polyoxometalate mineral with a bicapped Keggin anion from the Pickett Corral mine, Montrose County, Colorado, U.S.A. American Mineralogist, 104, 1851-1856.

Abstract:
Bicapite, KNa2Mg2(H2PV145+ O42)·25H2O, is a new mineral species (IMA2018-048) discovered at the Pickett Corral mine, Montrose County, Colorado, U.S.A. Bicapite occurs as square tablets up to about 0.2 mm on edge on montroseite-corvusite-bearing sandstone. Crystals are dark red-brown, often appearing black. The streak is orange, and the luster is vitreous. Bicapite is brittle, has a Mohs hardness of 1½, and displays one excellent cleavage on {100}. The measured density is 2.44(2) g/cm3. Bicapite is uniaxial (+), w = 1.785(5), e ≈ 1.81 (white light); pleochroism is red-brown; E > O, slight. The electron probe microanalysis and results of the crystal structure determination provided the empirical formula (based on 67 O apfu) (K1.23Na2.23Mg1.48)∑4.94[H2.51P1.02(V13.915+ Mo0.076+ )∑13.98O42]·25H2O. Bicapite is tetragonal, I4/m, with a = 11.5446(12) Å, c = 20.5460(14) Å, V = 2738.3(6) Å3, and Z = 2. The strongest four lines in the diffraction pattern are [d in Å (I) (hkl)]: 10.14 (100) (002,101); 2.978 (29) (134,206); 2.809 (11) (305); and 2.583 (11) (420,008). The atomic arrangement of bicapite was solved and refined to R1 = 0.0465 for 1008 independent reflections with I > 2sI. The structural unit is a [H2PV125+ O40(V5+O)2]7– heteropolyanion composed of 12 distorted VO6 octahedra surrounding a central PO4 tetrahedron and capped on opposite sides by two VO5 square pyramids; the structural unit is a modification of the a-isomer of the Keggin anion, [XM12O40]n-. Charge balance in the structure is maintained by the [KNa2Mg2(H2O)25]7+ interstitial complex. The name bicapite is in recognition of this being the only known mineral with a structure based on a bicapped Keggin anion. The discovery of bicapite and numerous other natural polyoxometalate compounds in the Colorado Plateau uranium/ vanadium deposits make that the most productive region found to date for naturally occurring polyoxometalate compounds.
Marco E. Ciriotti

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