View source for Siderite

{{Short description|Mineral composed of iron(II) carbonate}}
{{For|the type of meteorite|Iron meteorite}}
{{Infobox mineral
| name        = Siderite
| category    = [[Carbonate mineral]]
| boxwidth    = 
| boxbgcolor  = 
| image       = Harvard Museum of Natural History. Siderite. Gilman, Eagle Co., CO (DerHexer) 2012-07-20.jpg
| imagesize   = 260px
| alt         = 
| caption     = 
| formula     = FeCO<sub>3</sub>
| IMAsymbol   = Sd<ref>{{Cite journal|last=Warr|first=L. N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3 |pages=291–320|doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |s2cid=235729616 |doi-access=free}}</ref>
| strunz      = 5.AB.05
| dana        = 14.01.01.03
| system      = [[Trigonal]]
| class       = Hexagonal scalenohedral ({{overline|3}}m) <br/>[[H-M symbol]]: ({{overline|3}} 2/m)
| symmetry    = ''R''{{overline|3}}c
| unit cell   = ''a'' = 4.6916 <br> ''c'' = 15.3796&nbsp;[Å]; ''Z''&nbsp;=&nbsp;6
| color       = Pale yellow to tan, grey, brown, green, red, black and sometimes nearly colorless
| habit       = Tabular crystals, often curved; botryoidal to massive
| twinning    = Lamellar uncommon on{01{{overline|1}}2}
| cleavage    = Perfect on {01{{overline|1}}1}
| fracture    = Uneven to conchoidal
| tenacity    = Brittle
| mohs        = 3.75–4.25
| luster      = Vitreous, may be silky to pearly
| streak      = White
| diaphaneity = Translucent to subtranslucent
| gravity     = 3.96
| density     = 
| polish      = 
| opticalprop = Uniaxial (−)
| refractive  = ''n''<sub>ω</sub> = 1.875 <br> ''n''<sub>ε</sub> = 1.633
| birefringence = ''δ'' = 0.242
| pleochroism = 
| 2V          = 
| dispersion  = Strong
| extinction  = 
| length fast/slow =
| fluorescence= 
| absorption  =
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| other       = 
| alteration  = 
| references  = <ref name="handbook">{{cite book |title=Handbook of Mineralogy: Borates, Carbonates, Sulfates |year=2003 |publisher=Mineral Data Publishing |location=Tucson, Arizona |isbn=9780962209741 |url=https://rruff.info/doclib/hom/siderite.pdf |access-date=2022-11-30 |archive-url=https://web.archive.org/web/20220313194153/https://rruff.info/doclib/hom/siderite.pdf |archive-date=13 March 2022 |language=en |chapter=Siderite}}</ref><ref name="Mindat">{{Mindat |id=3647 |name=Siderite |access-date=2022-11-30}}</ref><ref name="Webmin">{{WebMineral |url=https://webmineral.com/data/Siderite.shtml |name=Siderite Mineral Data |access-date=2022-11-30}}</ref>
}}

'''Siderite''' is a [[mineral]] composed of [[iron(II) carbonate]] (FeCO<sub>3</sub>). Its name comes from the [[Ancient Greek]] word {{wikt-lang|grc|σίδηρος}} ({{grc-transl|σίδηρος}}), meaning "iron". A valuable [[iron ore]], it consists of 48% [[iron]] and lacks [[sulfur]] and [[phosphorus]]. [[Zinc]], [[magnesium]], and [[manganese]] commonly substitute for the iron, resulting in the siderite-[[smithsonite]], siderite-[[magnesite]], and siderite-[[rhodochrosite]] [[solid solution]] series.<ref name=Mindat/>

Siderite has [[Mohs scale of mineral hardness|Mohs hardness]] of 3.75 to 4.25, a [[specific gravity]] of 3.96, a white [[Streak (mineralogy)|streak]] and a [[vitreous lustre|vitreous]] or [[Lustre (mineralogy)#Pearly lustre|pearly luster]]. Siderite is [[Antiferromagnetism|antiferromagnetic]] below its [[Néel temperature]] of {{cvt|37|K|C|0}} that can assist in its identification.<ref>{{cite journal |last1=Frederichs |first1=T. |last2=von Dobeneck |first2=T. |last3=Bleil |first3=U. |last4=Dekkers |first4=M. J. |title=Towards the identification of siderite, rhodochrosite, and vivianite in sediments by their low-temperature magnetic properties |journal=Physics and Chemistry of the Earth, Parts A/B/C |date=January 2003 |volume=28 |issue=16–19 |pages=669–679 |doi=10.1016/S1474-7065(03)00121-9|bibcode=2003PCE....28..669F }}</ref>

It crystallizes in the [[trigonal crystal system]]; crystals are [[rhombohedral]] in shape, typically with curved and striated faces. It also occurs in masses. Color ranges from yellow to dark brown or black, the latter being due to the presence of manganese.

Siderite is commonly found in [[Hydrothermal circulation|hydrothermal]] [[Vein (geology)|veins]], and is associated with [[barite]], [[fluorite]], [[galena]], and others. It is also a common [[Diagenesis|diagenetic]] mineral in [[shale]]s and [[sandstone]]s, where it sometimes forms [[concretion]]s, which can encase three-dimensionally preserved [[fossils]].<ref>{{cite journal |first1=Russell |last1=Garwood |first2=Jason A. |last2=Dunlop |first3=Mark D. |last3=Sutton |year=2009 |title=High-fidelity X-ray micro-tomography reconstruction of siderite-hosted Carboniferous arachnids |journal=[[Biology Letters]] |volume=5 |issue=6 |pages=841–844 |doi=10.1098/rsbl.2009.0464 |pmid=19656861 |pmc=2828000}}</ref> In [[sedimentary rock]]s, siderite commonly forms at shallow burial depths and its elemental composition is often related to the [[Sedimentary depositional environment|depositional environment]] of the enclosing sediments.<ref>{{cite journal|last=Mozley |first=P. S. |date=1989 |title=Relation between depositional environment and the elemental composition of early diagenetic siderite |journal=Geology |volume=17 |issue=8 |pages=704–706|doi=10.1130/0091-7613(1989)017<0704:RBDEAT>2.3.CO;2 |bibcode=1989Geo....17..704M }}</ref> In addition, a number of recent studies have used the [[Oxygen isotopes|oxygen isotopic composition]] of sphaerosiderite (a type associated with [[soil]]s) as a [[Proxy (climate)|proxy]] for the [[Isotope|isotopic]] composition of [[meteoric water]] shortly after deposition.<ref>{{cite journal|last1=Ludvigson |first1=G. A. |last2=Gonzalez |first2=L. A. |last3=Metzger |first3=R. A. |last4=Witzke |first4=B. J. |last5=Brenner |first5=R. L. |last6=Murillo |first6=A. P. |last7=White |first7=T. S. |date=1998 |title=Meteoric sphaerosiderite lines and their use for paleohydrology and paleoclimatology |journal=Geology |volume=26 |issue=11 |pages=1039–1042|doi=10.1130/0091-7613(1998)026<1039:MSLATU>2.3.CO;2 |bibcode=1998Geo....26.1039L }}</ref> Evidence of the presence of siderite on Mars is being interpreted as a possible indicator of the presence of abundant water early in the climate history of that planet.<ref>Janice Bishop and M. Lane, ''Catching a glimpse of ancient Mars'', [[Science]], Vol. 388, April 18, 2025, p. 251. doi: 10.1126/science.adw4889 </ref><ref>Benjamin Tutolo et al., ''Carbonates identified by the Curiosity rover indicate a carbon cycle operated on ancient Mars'', Science, Vol. 388, April 18, 2025, p. 292. doi: 10.1126/science.ado9966 </ref><ref>Grossman, Lisa, ''[https://www.sciencenews.org/article/nasa-curiosity-rover-mars-missing-carbon A NASA rover finally found Mars’ missing carbon: The finding could help explain why Mars lost its habitable climate]'', [[Science News]], April 17, 2025 </ref>

== Carbonate iron ore ==<!-- 'Spathic iron ore' redirects here -->
Although [[carbonate]] iron ores, such as siderite, have been economically important for steel production, they are far from ideal as an ore. 

Their hydrothermal mineralisation tends to form them as small [[ore lens]]es, often following steeply [[dip (geology)|dip]]ping [[bedding plane]]s.{{efn-lr|Some siderite, along with [[goethite]], also forms in [[bog iron]] deposits,{{sfn|Sedimentary Geology|page=304}} but these are small and economically minor.}} This keeps them from being amenable to [[opencast mining|opencast working]], and increases the cost of working them by mining with horizontal [[stoping|stope]]s.{{sfnp|Jones|2011|page=34–35,37}} As the individual ore bodies are small, it may also be necessary to duplicate or relocate the pit head machinery, [[winding engine]], and pumping engine, between these bodies as each is worked out. This makes mining the ore an expensive proposition compared to typical [[ironstone]] or [[haematite]] opencasts.{{efn-lr|Both ironstones and [[banded iron formation]]s are sedimentary formations, thus the economically viable deposits may be considerable thicker and more extensive.<ref name="SG, 302" />}}<!-- is a serial comma needed after "considerable" to make sense regarding three items, or should "considerable" be changed to "considerably"? -->

The recovered ore also has drawbacks. The carbonate ore is more difficult to [[Smelting|smelt]] than a haematite or other oxide ore. Driving off the carbonate as carbon dioxide requires more energy and so the ore 'kills' the [[blast furnace]] if added directly. Instead the ore must be given a preliminary roasting step. Developments of specific techniques to deal with these ores began in the early nineteenth century, largely with the work of [[Sir Thomas Lethbridge, 2nd Baronet|Sir Thomas Lethbridge]] in [[Somerset]].<ref name="Jones, 17" /> His 'Iron Mill' of 1838 used a three-chambered concentric roasting furnace, before passing the ore to a separate reducing furnace for smelting. Details of this mill were the invention of Charles Sanderson, a steel maker of Sheffield, who held the patent for it.<ref>{{Cite patent
  |country=GB
  |number=7828
  |gdate=October 1838
  |title=Smelting Iron Ores
  |inventor=Charles Sanderson
}}</ref>

These differences between spathic ore and haematite have led to the failure of a number of mining concerns, notably the [[Brendon Hills Iron Ore Company]].{{sfnp|Jones|2011|page=99}}

Spathic iron ores are rich in manganese and have negligible phosphorus. This led to their one major benefit, connected with the [[Bessemer process|Bessemer steel-making process]]. Although the first demonstrations by Bessemer in 1856 were successful, initial attempts by others to replicate his method infamously failed to produce good steel.{{sfnp|Jones|2011|page=16}} Work by the metallurgist [[Robert Forester Mushet]] showed that the reason for the discrepancy was the nature of the Swedish ores that Bessemer had innocently used; they were very low in phosphorus. Using a typical European high-phosphorus ore in Bessemer's converter gave a poor quality steel. To produce high quality steel from a high-phosphorus ore, Mushet realised that he could operate the Bessemer converter for longer, burning off all the steel's impurities including the unwanted phosphorus, but also the carbon (which is an essential ingredient in steel), and then re-adding carbon, along with manganese, in the form of a previously obscure ferromanganese ore with no phosphorus, [[spiegeleisen]].{{sfnp|Jones|2011|page=16}} This created a sudden demand for spiegeleisen. Although it was not available in sufficient quantity as a mineral, steelworks such as that at [[Ebbw Vale Steelworks|Ebbw Vale]] in South Wales soon learned to make it from the spathic siderite ores.{{sfnp|Jones|2011|page=158}} For a few decades, spathic ores were therefore in demand and this encouraged their mining. In time though, the original 'acidic' liner of the Bessemer converter, made from siliceous sandstone or [[ganister]], was replaced by a 'basic' liner in the newer [[Sidney Gilchrist Thomas|Gilchrist Thomas process]]. This removed the phosphorus impurities as [[slag]] produced by chemical reaction with the liner, and no longer required spiegeleisen. From the 1880s, demand for the ores fell once again and many of their mines, including those of the [[Brendon Hills]], closed soon after.

== Gallery ==
<gallery widths="180px" heights="120px" >
Siderite late 1800s Redruth.jpg|Siderite from [[Redruth]], Cornwall, England
Galena-Quartz-Siderite-oldeuro-56c.jpg|Siderite crystals with galena and quartz. Size: {{cvt|6.2|x|4.1|x|3.6|cm|1}}
Chalcopyrite-Siderite-gha7a.jpg|Disc-shaped, brown siderite crystals perched upon chalcopyrites
SideriteTaillée.jpg|Cut siderite from Minas Gerais, Brazil. Size: {{cvt|5|x|3.2|mm}}
Siderite-64328.jpg|Colorado siderite, with sharp blades of olive-brown and minor accenting quartz
Siderite Concretion Carboniferous.JPG|Fossiliferous siderite concretion from the Lower Carboniferous
</gallery>

== Notes ==
{{Notelist-lr}}

== References ==
{{Reflist|colwidth=35em|refs=

<ref name="Jones, 17" >{{Cite book
  |title=The Brendon Hills Iron Mines and the West Somerset Mineral Railway
  |first=M. H.  |last=Jones
  |publisher=Lightmoor Press
  |year=2011
  |isbn=9781899889-5-3-2
  |pages=17–22
}}</ref>

<ref name="SG, 302" >{{Cite book
  |title=Sedimentary Geology
  |last1=Prothero  |first1=Donald R.
  |last2=Schwab  |first2=Fred
  |publisher=W. H. Freeman and Company  |location=New York
  |year=1996
  |isbn=0-7167-2726-9
  |ref={{harvid|Sedimentary Geology}}
  |pages=300–302
}}</ref>

}}

{{Commons category| Siderite}}

[[Category:Iron(II) minerals]]
[[Category:Carbonate minerals]]
[[Category:Calcite group]]
[[Category:Carbonates]]
[[Category:Trigonal minerals]]
[[Category:Minerals in space group 167]]
[[Category:Iron ores]]