IMA 2018-083 = cuatrocapaite-(NH4) / IMA 2018-084 = cuatrocapaite-(K)

database, nuove specie, discrediti,
ridefinizioni, classificazioni, ecc.
Rispondi
Avatar utente
Marco E. Ciriotti
Messaggi: 25412
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

IMA 2018-083 = cuatrocapaite-(NH4) / IMA 2018-084 = cuatrocapaite-(K)

Messaggio da Marco E. Ciriotti » mar 23 apr, 2019 21:02

Prossima pubblicazione.

Referenza:
▪ Kampf, A.R., Chukanov, N.V., Möhn, G., Dini, M., Molina Donoso, A.A., Friis, H. (2019): Cuatrocapaite-(NH4) and cuatrocapaite-(K), two new minerals from the Torrecillas mine, Iquique Province, Chile, related to lucabindiite and gajardoite. Mineralogical Magazine, 83, (in press).

Abstract:
The new minerals cuatrocapaite-(NH4) (IMA2018-083) and cuatrocapaite-(K) (IMA2018-084) are the NH4- and K-dominant members of a series with the general formula (NH4,K)3(NaMg□)(As2O3)6Cl6·16H2O. Both minerals were found at the Torrecillas mine, Iquique Province, Chile, where they occur as secondary alteration phases. Both minerals occur as hexagonal tablets up to about 0.3 mm in diameter. They are transparent, with vitreous lustre and white streak. For both, the Mohs hardness is ca. 2½, the crystals are somewhat flexible, but not elastic, the fracture is irregular and the cleavage is perfect on {001}. The measured densities are 2.65(2) and 2.76(2) g/cm3 for the NH4- and K-dominant species, respectively. Optically, cuatrocapaite-(NH4) is uniaxial (–) with ω = 1.779(3) and ε = 1.541(3) and cuatrocapaite-(K) is uniaxial (–) with ω = 1.777(3) and ε = 1.539(3) (white light). The minerals are insoluble in acids, but decompose in NaOH(aq). The empirical formulas, determined from electron-microprobe analyses, are (NH4)2.48Na1.66Mg0.87K0.09(As12O18.05)Cl5.88·16.02H2O and K2.68Na1.33Mg0.93(NH4)0.31(As12O18.01)Cl6.16·16.04H2O. The minerals are trigonal, space group R-3m; the cuatrocapaite-(NH4) cell parameters are a = 5.25321(19), c = 46.6882(19) Å, V = 1115.80(9) Å3 and Z = 1; the cuatrocapaite-(K) cell parameters are a = 5.2637(15), c = 46.228(8) Å, V = 1109.2(7) Å3 and Z = 1. The structures, refined for cuatrocapaite-(NH4) to R1 = 1.78% for 544 Io > 2I reflections, contain four types of layers: (1) a planar neutral As2O3 (arsenite) sheet, (2) an (NH4+,K+) layer that links adjacent arsenite sheets, (3) a Cl– layer placed on the As side of each arsenite and (4) a layer containing partially occupied Na, Mg and H2O sites that is flanked on either side by Cl layers. The layer sequence for the type 1, 2 and 3 layers is identical to the Cl–As2O3–K–As2O3–Cl layer sequence in the structures of lucabindiite and gajardoite.
Marco E. Ciriotti

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

Avatar utente
Marco E. Ciriotti
Messaggi: 25412
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: IMA 2018-083 = cuatrocapaite-(NH4) / IMA 2018-084 = cuatrocapaite-(K)

Messaggio da Marco E. Ciriotti » mer 24 apr, 2019 12:21

Tutte queste specie potrebbero essere accomunate nel gruppo della lucabindiite.

lucabindiite group

Cuatrocapaite-(K) K3(NaMg☐)(As3+2O3)6Cl6·16H2O trig P3m 5.2637 5.2637 46.228 90.00 120.00 90.00 1 1109.2
Cuatrocapaite-(NH4) (NH4)3(NaMg☐)(As3+2O3)6Cl6·16H2O trig P3m 5.25321 5.25321 46.6882 90.00 120.00 90.00 1 1115.8
Gajardoite KCa0.5As3+4O6Cl2·5H2O hex P6/mmm 5.2558 5.2558 15.9666 90.00 120.00 90.00 1 381.96
Lucabindiite KAs3+4O6(Cl,Br) hex P6/mmm 5.2386 5.2386 9.014 90.00 120.00 90.00 1 214.23
Russoite (NH4)As3+2O3Cl∙½H2O hex P622 5.259 5.259 12.590 90.00 120.00 90.00 2 301.55
Torrecillasite NaAs3+4O6Cl orth Pmcn 5.2580 8.0620 18.654 90.00 90.00 90.00 4 790.7

Le strutture non sono topologiche ma comunque simili (russoite e torrecillasite differiscono un po' di più).

Note: name “cuatrocapaite” is in allusion to the structure, which consists of four (cuatro in Spanish) different types of layers (capa in Spanish).
Marco E. Ciriotti

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

Rispondi

Chi c’è in linea

Visitano il forum: Nessuno e 4 ospiti