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Formula: Mg10Fe3+2(CO3)(OH)24.2H2O
Hydrated carbonate containing hydroxyl, hydrotalcite supergroup
Crystal System: Trigonal
Specific gravity: 2.32 to 2.42 measured, 2.26 calculated
Hardness: 1 to 2
Colour: Deep reddish brown, brown, straw-yellow; golden brown in transmitted light
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the Muskox Intrusion, Coppermine River area, Nunavut, Canada, coalingite has been recognised only in specimens
of drill core, predominantly in the serpentinite unit. Much, if not
all, of the coalingite appears to have formed in situ in the cores after collection. The pre-coalingite
material is referred to as thin brown
serpentine-magnetite veinlets, and
in another sample as reddish brown serpentine with
hematite. There is evidence that the Muskox coalingite was formed by in
situ alteration of closely associated hydrous iron oxides and sulphides
(AM 54.437-447).
At the type locality, the New Idria Serpentinite Asbestos deposits, Wright Mountain, Fresno county, California, USA,
coalingite has been identified in the surface weathering zone of the
serpentinite; it occurs as soft, reddish brown platelets, 0.1 to
0.2 mm in size, with resinous lustre. Individual grains are contaminated with either
chrysotile or pyroaurite,
intimately intergrown with the coalingite.
Indications are that coalingite forms in situ from pre-existing brucite,
an important constituent of the serpentinite, with up to 18 weight
per cent iron in brucite from this body,
sufficient to form coalingite directly without the introduction of iron from
an external source. The data strongly indicate that coalingite is formed by the oxidation and carbonation of
iron-rich brucite in the surface weathering
zone of the serpentinite.
Artinite and hydromagnesite are
also found in the weathering zone, but are decidedly later and probably precipitated directly from magnesium-rich ground
waters
(AM 50.1893-1913).
Other associated minerals include lizardite,
antigorite,
hydrotalcite-pyroaurite,
magnetite, chromite,
uvarovite and calcite
(HOM).
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