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Formula: Fe2+Fe3+2S4
Sulphide, linnaeite subgroup,
thiospinel group,
spinel supergroup, forms a series with
violarite
Crystal System: Isometric
Specific gravity: 4.049 measured, 4.079 calculated
Hardness: 4 to 4½
Streak: Black
Colour: Metallic pinkish, tarnishing to a metallic blue, sooty black when amorphous
Magnetism: Strongly magnetic
Common impurities: Cu,Ni,Zn,Mn,Cr,Sb,As
Environments
Sedimentary environments
Hydrothermal environments
Greigite is formed in lacustrine beds and in hydrothermal vein deposits; it is formed in magnetotactic (exhibiting
movement in response to a magnetic field) bacteria, and by sulphate-reducing bacteria
(HOM).
Common associates include calcite,
chlorite,
dolomite, galena,
marcasite,
montmorillonite,
pyrite and sphalerite
(Mindat).
Localities
At Zacatecas, Mexico, greigite is associated with sphalerite,
pyrite, marcasite,
galena, calcite and
dolomite
(HOM).
At Lojane, Lipkovo Municipality, North Macedonia, the country rocks are
serpentinites and
serpentinised
peridotites intruded by
granites,
syenites and
rhyolites. Greigite
has been found dispersed, in very small quantities, throughout the ore bodies. In most cases it occurs as
fine-grained globular
aggregates within stibnite. It also occurs within fractures in
stibnite and, rarely, in the
gangue minerals.
Nickel possibly replaces some of the ferrous iron in the greigite
structure, and
influences the colour of greigite, the characteristic pink colour being more pronounced with an increased
nickel content.
Greigite formed in two generations, one as relatively large individual crystals which are corroded by
stibnite, and another as very fine inclusions and globular aggregates in
fractures in the
stibnite. It appears that greigite was deposited before
realgar in the paragenetic sequence
(AM 51, 209-215).
At the Mudd Mine, West Baker, Kramer Borate deposit, Boron, Kramer District, Kern county, California, USA,
greigite has been
found as tiny inclusions in crystals of kernite. Associated as included
minerals are montmorillonite,
chlorite,
biotite, and single euhedral crystals of
dolomite,
calcite and searlesite. In
contrast to the widespread occurrence in the Four Corners area, greigite has been positively identified
only from this single occurrence in the
Kramer borate district.
It seems probable that greigite was formed by bacterial reduction of
iron-bearing waters in essentially anaerobic bottom
sediments of an alkaline lake
(AM 49.543-555).
At the type locality, Four Corners No. 3, 4 & 5 wells, Kramer Junction, East Kramer Borate area, East Kramer
Mining District, San Bernardino county, California, USA, greigite was discovered in cores recovered from
lacustrine sediments. The
greigite-bearing sediments are overlain by 650 to 800 feet of alluvium, and underlain by
sandstones and
conglomerates.
The lake beds are composed of interbedded calcareous clays, silts and
fine- to medium-
grained arkosic sands. Greigite is restricted to
clay and fine silt layers, being completely absent from the sands and
other coarse-grained
material. Associated minerals include montmorillonite,
chlorite, calcite,
colemanite, veatchite,
orpiment and realgar. The
greigite sample
concentrated for analysis also contained a small amount of marcasite in
close association. The only other iron sulphide observed in the drill cores
was a small amount of pyrite, that
was not directly associated with greigite.
In the Kramer district, greigite appears to have formed with borax
in the temperature
range 25oC to 35oC, and to have remained as a stable or metastable phase after conversion of
the
borax to kernite, which occurs at
58+/-5oC and a depth of 2500+/-500 feet
(AM 49.543-555).
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