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Formula: Fe(CO3)
Carbonate
Crystal System: Trigonal
Specific gravity: 3.96 measured 3.932 calculated
Hardness: 4 to 4½
Streak: White
Colour: Yellowish white, yellowish brown to dark brown
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Common impurities: Mn,Mg,Ca,Zn,Co
Environments:
Pegmatites
Sedimentary environments
Metamorphic environments
Hydrothermal environments
Pelosiderite is a fine grained, concretionary variety of siderite.
Siderite is frequently found mixed with clay minerals, in
concretions with
concentric layers. As black-band ore it is found, contaminated by carbonaceous material, in extensive stratified
formations in shale and commonly associated with coal measures. It is
also formed
by the action of iron-rich solutions on
limestone. Siderite is a common
vein mineral associated
with silver minerals, pyrite,
chalcopyrite,
tetrahedrite and
galena in the oxidation zone of
hypothermal (high temperature) hydrothermal veins.
Siderite may be found in
limestone, and in the alkaline
syenite
pegmatites of Mont Saint-Hilaire, Canada
(R&M 93.2.147).
Localities
At Mount Moliagul, Moliagul, Central Goldfields Shire, Victoria, Australia, aggregates to 3 cm of siderite crystals
are found with calcite in cavities in quartz
(AJM 21.1.44).
At Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, siderite
pseudomorphs after serandite have
been found
(KL p159).
The Bairendaba Ag-polymetallic deposit, Hexigten Banner, Chifeng City, Inner Mongolia, China, is a mesothermal
magmatic-hydrothermal vein-type silver -
lead - zinc deposit, hosted in
Hercynian (about 419 to 299 million years ago) quartz
diorite.
It is suggested that, with decreasing temperature, mineral compositions changed progressively from
tungstate and oxide, to diatomic sulphide, to simple sulphide, to an
antimony sulphosalt mineral, and finally to an
antimonide.
Siderite has been found at Bairendaba as platy, yellow-brown, lenticular crystals to 1 or 2 cm, associated
with green cubic fluorite and corroded purple cubic
fluorite, and also as large, platy crystals to 5 cm with
fluorapatite and cubic pyrite
(Minrec 53.347-359).
At the Panasquiera mine, Portugal, siderite pseudomorphs after
apatite have been found
(KL p157).
At the Turt mine, Muramures, Romania, siderite pseudomorphs after
calcite have been found
(KL p158).
At the Aggenys mine, South Africa, siderite pseudomorphs after
sphalerite have been found
(KL p160).
At Teller county, Colorado, USA, a goethite
pseudomorph after siderite has been found with
microcline
(KL p145).
At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the
pegmatites are beryl-type
rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most
complex zonation and diverse mineralogy of any of the Keyes
pegmatites. Six zones are distinguished, as follows, proceeding
inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase
border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite
wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite
outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite
middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to
1.2 meters in size that were altered to vuggy
albite-muscovite with
fluorapatite crystals. This unit presumably was the source of the
albite, muscovite,
fluorapatite, quartz and other
crystallised minerals found in pieces of vuggy albite
rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including
tourmaline, graftonite,
triphylite, vivianite,
pyrite, pyrrhotite, and
beryl crystals to 30.5 cm long and 12.7 cm across.
Siderite occurs as blocky to disc-shaped orange crystals in vuggy albite at the Keyes No. 1 mine. Associated
minerals include quartz, pyrite and
muscovite
(R&M 97.4.325).
At the Kabwe mine, Central Province, Zambia, siderite has been found associated with
smithsonite (R&M 94.2.134).
Alteration
chalcopyrite, arsenopyrite, CO2
and O2 to Fe-tennantite, siderite and
sulphur
10CuFeS2 + 4FeAsS + 4CO2 + 8O2 → Cu10Fe2As4S13 +
4Fe(CO3) + 11/2S2
(CM 28.725-738)
olivine and CO2 to enstatite-
ferrosilite and
magnesite-siderite
(Mg,Fe)2SiO4 + CO2 → (Mg,Fe2+)SiO3 +
(Mg,Fe)CO3
(DHZ 2A p139)
siderite, oxygen and H2O to hematite and silicic acid
2Fe2CO3 + O2 + 4H2O → 2Fe2O3 +
2H2CO3
On prolonged exposure to the air Fe2+ compounds are oxidised to Fe3+ compounds according
to reactions such as the one above
(KB p334).
siderite and quartz to fayalite
and CO2
2Fe(CO3) + SiO2 = Fe2+2(SiO4) + 2CO2
(DHZ 1A p265)
Mg-rich siderite and quartz to olivine,
orthopyroxene and CO2
3(Fe,Mg)(CO3)→ (Fe,Mg)2SiO4 + 2SiO2 →
(Fe,Mg)2SiO4 + 3CO2
(DHZ 1A p266)
Fe-tetrahedrite, siderite and
sulphur to chalcopyrite,
stibnite, CO2 and O2
Cu10Fe2Sb4S13 + 8Fe(CO3) + 13/2S2 → 10CuFeS2
+ 2Sb2S3 + 8CO2 + 4O2
(CM 28.725-738)
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