Home > Mineral Abstracts > CanMin Vol. 37, pp. 893-899 (1999)




Vol. 37, pp. 893-899 (1999)



Khomyakovite and manganokhomyakovite, two new members of the eudialyte group
from Mont Saint-Hilaire, Quebec, Canada


Ole Johnsen
Geological Museum, University of Copenhagen,
Oster Voldgade 5-7, DK-1350 Copenhagen, Denmark



Robert A. Gault, Joel D. Grice and T. Scott Ercit
Research Division, Canadian Museum of Nature,
P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada


ABSTRACT

     Khomyakovite, ideally Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2 and manganokhomyakovite, ideally Na12Sr3Ca6Mn3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2 are two new members of the eudialyte group from Mont Saint-Hilaire, Quebec. They occur as orange to orange-red, pseudo-octahedral crystals ranging in size from 0.5mm (khomyakovite) to 5mm (manganokhomyakovite). Associated minerals include, for khomyakovite: analcime, annite, calcite, natrolite, pyrite, and titanite, and for manganokhomyakovite: aegirine, albite, analcime, annite, cerussite, galena, kupletskite, microcline, molybdenite, natrolite, pyrite, pyrrhotite, sodalite, sphalerite, titanite, w÷hlerite and zircon. Both minerals are transparent to translucent, with a vitreous luster and white streak. They are brittle, with a hardness of 5-6 (Mohs scale). They have no cleavage, no parting and an uneven fracture. They are uniaxial negative, for khomyakovite: w = 1.6279(5) and e = 1.6254(5), and for manganokhomyakovite:
w = 1.629(1) and e = 1.626(2). They are trigonal, space group R3m. For khomyakovite: a 14.2959(8), c 30.084(3) Å, V5324.6(7) ┼3, and for manganokhomyakovite: a 14.282(3), c 30.12(1) Å, V53206(3) Å3, Z = 3.

     The strongest X-ray powder-diffraction lines, measured for manganokhomyakovite [d in Å (I)(hkl)] are:


11.500(90)(101)
9.535(70)(012)
6.452(50)(104)
6.072(50)(021)

5.735(50)(202)
3.406(50)(131)
3.213(50)(208)
3.167(50)(217)

 
2.980(100)(315)
2.856(50)(104)


     The infrared spectrum of manganokhomyakovite is given. An electron-microprobe analysis of the khomyakovite crystal used for single-crystal work gave:


Na2O - 11.35
K2O - 0.52
MgO - 0.04
CaO - 10.42

MnO - 1.63
FeO - 4.33
SrO - 8.45
Al2O3 - 0.09

La2O3 - 0.21
Ce2O3 - 0.18
SiO2 - 43.70
TiO2 - 0.11

ZrO2 - 10.62
HfO2 - 0.18
Nb2O5 - 1.33
Ta2O5 - 0.02

WO3 - 3.80
Cl - 0.67
H2O - 0.87
O = Cl - 0.15


total 98.37 wt.%


     The proportion of H2O was calculated by stoichiometry from the structure analysis. The empirical formula of khomyakovite, based on 78.70 anions as determined in the structure analysis is:


(Na12.26Ca0.33K0.38Sr0.13REE0.03)S13.05(Sr2.78Na0.22)S3 Ca6


(Fe2.05Mn0.75Mg0.03)S2.86 (Zr2.94Ti0.05Hf0.03)S3.02 (W0.56Nb0.34)S0.90


(Si24.78Al0.06)S24.84 O73(O,OH,H2O)3.70 (OH1.36Cl0.64)S2.

     For manganokhomyakovite, an average of four electron-microprobe analyses gave:


Na2O - 10.37
(10.05-10.59)
K2O - 0.41
(0.37-0.45)
CaO - 10.20
(10.08-10.35)
MnO - 4.21
(3.91-4.38)

FeO - 2.58
(2.40-2.65)
SrO - 9.17
(8.63-9.63)
Al2O3 - 0.02
(0.00-0.05)
La2O3 - 0.12
(0.00-0.27)

Ce2O3 - 0.20
(0.00-0.30)
SiO2 - 42.98
(42.51-43.39)
TiO2 - 0.02
(0.00-0.07)
ZrO2 - 10.43
(10.40-10.50)

HfO2 - 0.17
(0.16-0.19)
Nb2O5 - 1.58
(1.32-2.05)
Ta2O5 - 0.03
(0.00-0.05)
WO3 - 4.48
(3.66-4.83)

Cl - 0.84
(0.78-0.89)
H2O - 0.83
O = Cl - 0.19
total 98.45 wt.%



     The proportion of H2O was calculated by stoichiometry from the crystal-structure relationship with khomyakovite, confirmed by TGA and IR data. The empirical formula for manganokhomyakovite, based on 78.70 anions as found in the crystal structure of khomyakovite, is:


(Na11.51K0.30Ca0.25Sr0.04REE0.07)S12.17 Sr3Ca6 (Mn2.04Fe1.23)S3.27


(Zr2.91Hf0.03Ti0.01)S2.95 (W0.66Nb0.41Ta0.01)S1.08 (Si24.60Al0.01)S24.61


O73(O,OH,H2O)3.70 (OH1.19Cl0.81)S2

     For khomyakovite, Dcalc. = 3.14 g/cm3, and for manganokhomyakovite,
Dcalc. = 3.17 g/cm3 and Dmeas. = 3.13(3) g/cm3. Both these minerals possess the eudialyte structure. Single-crystal data for khomyakovite show that W dominates over Nb in M(3), and Sr over Na in Na(4). M(2) is dominated by Fe in khomyakovite, and by Mn in manganokhomyakovite.

Keywords: khomyakovite, manganokhomyakovite, eudialyte, new mineral species, crystal structure, Mont Saint-Hilaire, Quebec, Canada.



© 1999  The Canadian Mineralogist