Description and crystal structure of Manganlotharmeyerite, Ca(Mn3+,?,Mg)2{AsO4,[AsO2 (OH 2]}2(OH,H2O)2, from the Starlera Mn deposit, Swiss Alps, and a redefinition of lotharmeyerite
- Author(s)
- Joel Brugger, Sergey V. Krivovichev, Uwe Kolitsch, Nicolas Meisser, Michael Andrut, Stefan Ansermet, Peter Carman Burns
- Abstract
Manganlotharmeyerite, Ca(Mn3+,□,Mg 2{AsO4,[AsO2(OH)2]}2 (OH,H2O)2, is a new member of the tsumcorite group of minerals, of general formula Me(1)Me(2)2(XO4 2(OH,H2O)2, in which Me(1) represents Pb2+, Ca2+, Na+ and Bi3+, Me(2) represents Fe3+, Mn3+, Cu2+, Zn2+, Co2+, Ni2+, Al3+ and Mg2+, and X can be P5+, As5+, V5+ or S6+. Manganlotharmeyerite occurs with sailaufite, (Ca,Na,□ 2Mn3O2(AsO4)2(CO 3 •,3H2O,
tilasite and calcite in discordant veinlets within massive braunite
ores at the Starlera Mn deposit in the Eastern Alps of Switzerland.
Manganlotharmeyerite and the associated arsenates are the product of the
latest stage of As remobilization during retrograde Alpine metamorphism
of Triassic carbonate-hosted, syngenetic exhalative Mn-ores.
Manganlotharmeyerite forms elongate platy crystals and aggregates up to 1
mm in length, but optically homogeneous crystals do not exceed 100 μm
in length. The mineral has a Mohs hardness of about 3, with a Dcalc of 3.75(2) and a Dmeas of 3.77(2) g/cm3;
it is brittle, with an irregular fracture and a distinct cleavage
parallel to {001}. Manganlotharmeyerite is transparent to translucent
with an adamantine luster. It is brown-red to dark reddish orange in
color, and has a light brown streak. The new mineral species is biaxial
positive, with α 1.785(5), β 1.814(5) and γ 1.854(5), 2V(meas.) about
85°, 2V(calc.) 82°, dispersion r < v weak. The average composition of
the mineral, measured with an electron microprobe, is [wt%]: V2O5 0.67, As2O5 53.41, MgO 3.95, Mn2O3 16.70, CaO 12.42. Fe2O3, 0.91, NiO 1.07, minor quantities (< 1 wt%) of Al2O3, SrO, Na2O, CoO, and ZnO, H2Ocalc 8.84, sum 99.3, resulting in the empirical chemical formula (Ca0.94Sr0.01Na0.01 (Mn3+ 0.45□0.26Mg0.20Ni 0. 03 Fe0.02Zn0.02Al0.01Co0.01 2(As0.98V0.02)2O 10H4.16. The structural chemical formula of the mineral derived on the basis of the crystal- structure refinement is Ca(Mn3+ 0.59□0 .24Mg2+ 0.17)2{(AsO4 0.76[AsO2(OH)2]0.24}2[(OH 0. 59(H2O)0.41]2. Manganlotharmeyerite is monoclinic, C2/m, a 9.043(1), b 6.2314(7), c 7.3889(9) Å, β 116.392(2)°, V 372.99(9) Å3 and Z = 2. Single-crystal structure refinement (R1
= 0.025) confirmed isotypy with the tsumcorite structure. The strongest
ten lines in the X-ray powder-diffraction pattern [d in Å (I)(hkl)]
are: 4.93(80) (1̄10), 4.61(50)(111), 3.426(60 (2̄02), 3.182(100)(1̄12),
3.122 (50)(020), 2.927(70)(201), 2.822(70 (02̄1), 2.718(80)(3̄11),
2.555(100)(2̄21,3̄12), 2.134(70 (202,221). Unit-cell parameters from the
powder-diffraction data are: a 9.074(5), b 6.239(3), c 7.406(4), β
116.60(3)°. The nomenclature of members of the tsumcorite group with
Me(1) = Ca and X = As (lotharmeyerite subgroup) is based on the occupant
of the Me(2) site. Manganlotharmeyerite represents the Mn3+-
dominant member of the group, and lotharmeyerite is redefined to
represent the Zn-dominant member. The lotharmeyerite subgroup now
contains six phases: cabalzarite with Me(2) = Mg, ferrilotharmeyerite
(Fe3+), cobaltlotharmeyerite (Co), nickellotharmeyerite (Ni), lotharmeyerite (Zn) and manganlotharmeyerite (Mn3+).
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- University of Adelaide, Saint Petersburg State University, Musée cantonal de Géologie Lausanne, University of Notre Dame
- Journal
- The Canadian Mineralogist
- Volume
- 40
- Pages
- 1597-1608
- No. of pages
- 12
- ISSN
- 0008-4476
- DOI
- https://doi.org/10.2113/gscanmin.40.6.1597
- Publication date
- 2002
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1051 Geology, Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/fa6b4cf4-975f-4b68-84d5-6feb492c0dc2