Crystal chemistry of johillerite

Autor(en)

Natalya N. Koshlyakova, Natalia V Zubkova, Igor V Pekov, Gerald Giester, Evgeny G. Sidorov

Abstrakt

Johillerite, an anhydrous arsenate member of the alluaudite group with the idealized crystal chemical formula

^A(2)Na

^A(1)Cu

^MMg

₃(TAsO

₄)

₃, is an abundant mineral in the exhalations of the Arsenatnaya fumarole on the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Kamchatka, Russia. Chemical variations of johillerite from Tolbachik were studied and the crystal structure was solved for three samples that represent different chemical varieties of the mineral. Johillerite forms a continuous solid-solution system with badalovite, Na

₂Mg

₂Fe

³⁺(AsO

₄)

₃, and nickenichite, Na(□,Cu)(□,Ca)(Mg,Fe)

₃(AsO

₄)

₃, and a discontinuous solid solution with bradaczekite, NaCu

₄(AsO

₄)

₃. The major substitution schemes are: (1)

^MMg=MCu

²⁺; (2)

^ACu

²⁺+M

²⁺=ANa

⁺+M

³⁺; (3)

^ANa

⁺+M

²⁺=

^A□

⁰+M

³⁺; and (4)

^ACu

²⁺+2M2+=

^A□

⁰+ 2M

³⁺. The T sites are occupied by As

⁵⁺ with only minor admixtures of other constituents (P, V, S, Si). Structurally studied johillerite crystals (monoclinic, C2/c) have the following crystal chemical formulae: (1)

^A(2)′Na

_0.75

^A(1)′Cu

_0.85

^A(1)Na

_0.13

^M(1)(Mg

_0.91Fe

_0.09)

^M(2)(Mg

_1.60Fe

_0.34Cu

_0.06)(AsO

₄)

₃; (2)

^A(2)′Na

_0.84

^A(1)′Cu

_0.68

^A(1)Na

_0.33

^M(1)(Mg

_0.68Zn

_0.32)

^M(2)(Mg

_0.90Cu

_0.62 Fe

_0.16Al

_0.08)(AsO

₄)

₃; (3)

^A(2)′Na

_0.91

^A(1)′Cu

_0.98

^M(1)(Mg

_0.74Cu

_0.16Zn

_0.10)

^M(2)(Mg

_1.34Cu

_0.52Fe

_0.14)(AsO

₄)

₃. Mg and Zn prefer the M(1)O

₆ octahedra rather than the M(2)O

₆, whereas Fe

³⁺ and Al

³⁺ mainly concentrate at the M(2) site.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Russian Academy of Sciences, Lomonosov Moscow State University (MSU)

Journal

The Canadian Mineralogist

Band

56

Seiten

189-201

Anzahl der Seiten

13

ISSN

0008-4476

DOI

https://doi.org/10.3749/canmin.1700075

Publikationsdatum

03-2018

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/52ea0b0c-44cf-4f59-a89b-bbbda394d77d