Siderite

tetrahedrite

chalcopyrite

Formula: Fe(CO3) carbonate
Specific gravity: 3.7 to 3.9
Hardness: 4 to 4½
Streak: White
Colour: Yellowish white, yellowish brown to dark brown
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Pegmatites
Carbonatites (common)
Metamorphic environments
Hydrothermal environments

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).

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

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)

Common impurities: Mn,Mg,Ca,Zn,Co

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