Grimmite, NiCo 2 S 4 , a new thiospinel from Příbram, Czech Republic
2021
Abstract. The new mineral grimmite, NiCo 2 S 4 , was found in
siderite–sphalerite gangue at the dump of shaft no. 9, one of the mines in
the abandoned Přibram uranium and base-metal district, central
Bohemia, Czech Republic. The new mineral occurs as rare idiomorphic to
hypidiomorphic grains up to 200 µm × 70 µm in size or veinlet
aggregates. In reflected light, grimmite is creamy grey with a pinkish tint.
Pleochroism, polarising colours and internal reflections were not observed.
Reflectance values of grimmite in the air ( R %) are 42.5 at 470 nm, 45.9
at 546 nm, 47.7 at 589 nm and 50.2 at 650 nm). The empirical formula for
grimmite, based on electron-microprobe analyses ( n= 13), is
Ni 1.01 (Co 1.99 Fe 0.06 Pb 0.01 Bi 0.01)Σ2.07 S 3.92 . The ideal formula is NiCo 2 S 4 ; requires Ni 19.26,
Co 38.67, and S 42.07; and totals 100.00 wt %. According to the single-crystal
X-ray diffraction data ( Robs=0 .0489), grimmite is cubic, Fd–3 m , a=9 .3933(9), with V=828 .81(14) A 3 and Z=8 . The calculated
density is 4.96 g cm −3 . The strongest reflections of the calculated
powder X-ray diffraction pattern [ d , A (I)(hkl)] are 3.3210 (75) (220),
2.7116 (7) (222), 2.3483 (81) (400), 1.9174 (27) (422), 1.6605 (100) (440),
1.4852 (11) (620) and 1.3558 (15) (444). Grimmite is named after Johann Grimm
(24 June or 24 July 1805 to 26 June 1874), the former director of the
Přibram Mining College. The association of sulfides and
sulfarsenides was found with grimmite. Essentially non-zoned coarse-grained
siderite encloses idiomorphic crystals and/or aggregates of red sphalerite I
and zoned skutterudite-group minerals. Skutterudites (skutterudite,
niklskutterudite and ferroskutterudite) are usually strongly corroded and
replaced by younger phases. Relics of skutterudite are rimmed by nickeline
and later on by gersdorffite with rare domains of glaucodot and
arsenopyrite, whereas completely leached parts of skutterudite crystals are
filled up by quartz containing small isolated grains and aggregates of
pyrite, sphalerite II, grimmite, galena, ullmannite, bismuthinite, parkerite
and jaipurite, the latter being rarely enclosed in grimmite.
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