Editing Strontianite

{{Short description|Rare carbonate mineral and raw material for the extraction of strontium}}
{{Use dmy dates|date=April 2022}}
{{Infobox mineral
| name        = Strontianite
| boxwidth    = 
| boxbgcolor  = 
| image       = Mineraly.sk - stroncianit.jpg
| imagesize   = 260px
| alt         = 
| caption     = Strontianite from [[Slovakia]]
| category    = [[Carbonate minerals]]
| formula     = SrCO<sub>3</sub> 
| IMAsymbol   = Str<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>
| molweight   = 147.63 g/mol 
| strunz      = 5.AB.15 (10 ed) <br /><small>5/B.04-20 (8 ed)</small>
| dana        = 14.01.03.03
| system      = [[Orthorhombic]]
| class       = Dipyramidal (mmm) <br />[[H-M symbol]]: (2/m 2/m 2/m)
| symmetry    = ''Pmcn''
| unit cell   = a = 5.1&nbsp;[[angstrom|Å]], b = 8.4&nbsp;Å <br />c = 6.0&nbsp;Å; Z&nbsp;=&nbsp;4
| color       = Colourless, white, gray, light yellow, green or brown; colourless in transmitted light
| habit       = Prismatic, acicular, pseudo hexagonal, columnar to fibrous, granular, massive
| twinning    = Very common, usually contact, rarely penetration, also repeated
| cleavage    = {110} nearly perfect, {021} poor, {010} traces
| fracture    = Subconchoidal to uneven 
| tenacity    = Brittle 
| mohs        = {{frac|3|1|2}} 	
| lustre      = Vitreous, resinous on breaks, greasy 
| streak      = White			
| diaphaneity = Transparent to translucent
| gravity     = 3.74 to 3.78 Transparent versions are heavier than the other ones
| density     = 
| polish      = 
| opticalprop = Biaxial (−) 
| refractive  = n<sub>α</sub> = 1.52, n<sub>β</sub> = 1.66, n<sub>γ</sub> = 1.67 
| birefringence = 0.15 
| pleochroism = 
| 2V          = Measured: 7°, Calculated: 12° to 8° 
| dispersion  = 
| extinction  = 
| length fast/slow =
| fluorescence = Almost always fluorescent
| absorption  = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = Soluble in dilute HCl 
| impurities  = 
| alteration  = Celestine SrSO<sub>4</sub>
| other       = 
| prop1       = 
| prop1text   = 
| references  = <ref name=Dana>Gaines et al (1997) Dana’s New Mineralogy Eighth Edition.  Wiley</ref><ref name=Mindat>[http://www.mindat.org/min-3805.html Strontianite on Mindat.org retrieved 23/08/11]
</ref><ref name=Webmin>{{cite web|url=http://www.webmineral.com/data/Strontianite.shtml|title=Strontianite Mineral Data|first=Dave|last=Barthelmy|access-date=August 23, 2011}}</ref><ref name=HOM>{{cite web|url=http://rruff.info/doclib/hom/strontianite.pdf|title=Strontianite in the Handbook of Mineralogy |access-date=August 24, 2011}}</ref>
}}

'''Strontianite''' ([[Strontium|Sr]][[Carbon|C]][[Oxygen|O]]<sub>3</sub>) is an important raw material for the extraction of [[strontium]]. It is a rare [[carbonate mineral]] and one of only a few strontium minerals.  It is a member of the aragonite group.

Aragonite group members:<ref name=Dana/> [[aragonite]] (CaCO<sub>3</sub>), [[witherite]] (BaCO<sub>3</sub>), strontianite (SrCO<sub>3</sub>), [[cerussite]] (PbCO<sub>3</sub>)

The ideal formula of strontianite is SrCO<sub>3</sub>, with [[molar mass]] 147.63 g,<ref name=Webmin/> but [[calcium]] (Ca) can substitute for up to 27% of the strontium (Sr) [[Ion|cations]], and [[barium]] (Ba) up to 3.3%.<ref name=Dana/>

The mineral was named in 1791 for the locality, [[Strontian]], Argyllshire, Scotland, where the element [[strontium]] had been discovered the previous year.<ref name=Dana/>  Although good mineral specimens of strontianite are rare, strontium is a fairly common [[Chemical element|element]], with abundance in the [[Crust (geology)|Earth's crust]] of 370 parts per million by weight, 87 parts per million by [[Mole (unit)|moles]], much more common than [[copper]] with only 60 parts per million by weight, 19 by moles.<ref name=Chemicool>{{cite web|url=http://www.chemicool.com/elements/strontium.html|title=Strontium|access-date=August 24, 2011}}</ref> 
Strontium is never found free in nature. The principal strontium ores are [[Celestine (mineral)|celestine]] SrSO<sub>4</sub> and strontianite SrCO<sub>3</sub>.  The main commercial process for strontium metal production is [[Redox|reduction]] of [[strontium oxide]] with [[aluminium]].<ref name=Chemicool/>

== Unit cell ==
Strontianite is an [[Orthorhombic crystal system|orthorhombic]] mineral, belonging to the most symmetrical class in this system, 2/m 2/m 2/m, whose general form is a [[Rhombus|rhombic]] [[Bipyramid|dipyramid]].  The [[space group]] is Pmcn.  There are four formula units per [[unit cell]] (Z = 4) and the [[Crystal structure#Lattice systems|unit cell parameters]] are a = 5.1 Å, b = 8.4 Å, c = 6.0 Å.

== Structure ==
Strontianite is [[isostructural]] with [[aragonite]].<ref name=MOM>Klein and Hurlbut (1993) Manual of Mineralogy 21st Edition.  Wiley</ref>  When the CO<sub>3</sub> group is combined with large [[divalent]] [[Ion|cations]] with [[Ionic radius|ionic radii]] greater than 1.0&nbsp;Å, the radius ratios generally do not permit stable [[Coordination number|6-fold coordination]].  For small cations the structure is [[Rhombohedron|rhombohedral]], but for large cations it is [[Orthorhombic crystal system|orthorhombic]].  This is the aragonite structure type with [[space group]] Pmcn.  In this structure the CO<sub>3</sub> groups lie perpendicular to the c [[Crystal structure|axis]], in two structural planes, with the CO<sub>3</sub> triangular groups of one plane pointing in opposite directions to those of the other.<ref name=MOM/> These layers are separated by layers of cations.<ref name=Dana/>

The CO<sub>3</sub> group is slightly non-planar; the [[carbon]] [[atom]] lies 0.007 Å out of the plane of the [[oxygen]] atoms.  The groups are tilted such that the angle between a plane drawn through the oxygen atoms and a plane parallel to the [[Crystal structure#Unit cell|a-b unit cell plane]] is 2°40’.<ref name=AM56>De Villiers, Johan P R (1971) Crystal Structures of Aragonite, Strontianite and Witherite.  The American Mineralogist 56:758</ref>

== Crystal form ==

Strontianite occurs in several different [[Crystal habit|habits]].  Crystals are short [[Prism (geometry)|prismatic]] parallel to the c axis and often [[Acicular (crystal habit)|acicular]].<ref name=Dana/><ref name=Mindat/><ref name=HOM/>  [[Calcium]]-rich varieties often show steep [[Pyramid (geometry)|pyramidal]] forms.<ref name=Dana/>  Crystals may be pseudo [[hexagon]]al<ref name=Dana/><ref name=Mindat/><ref name=HOM/> due to equal development of different forms.<ref name=Mindat/>  Prism faces are striated horizontally.<ref name=Dana/><ref name=Mindat/>  The mineral also occurs as columnar to fibrous, granular or rounded masses.<ref name=Dana/><ref name=Mindat/><ref name=HOM/>

{{multiple image
 | align     = center
 | direction = horizontal
 | width     = 180
 | image1    = Strontianite-Calcite-Fluorite-274999.jpg|thumb
 | caption1  = Radial aggregate of strontianite
 | image2    = Strontianite-283289.jpg|thumb
 | caption2  = Acicular strontianite in spherical aggregates
 | image3    = Strontianite-ww3c.jpg|thumb
 | caption3  = Strontianite in pseudo-hexagonal crystals
}}

== Optical properties ==
Strontianite is colourless, white, gray, light yellow, green or brown, colourless in transmitted light.  It may be longitudinally zoned. It is transparent to translucent, with a vitreous (glassy) [[Lustre (mineralogy)|lustre]], resinous on broken surfaces, and a white [[Streak (mineralogy)|streak]].

It is a [[Birefringence#Positive or negative|biaxial(−)]] mineral. The direction perpendicular to the plane containing the two [[Optic axis of a crystal|optic axes]] is called the optical direction Y. In strontianite Y is parallel to the b crystal axis. The optical direction Z lies in the plane containing the two optic axes and bisects the acute angle between them. In strontianite Z is parallel to the a crystal axis. The third direction X, perpendicular both to Y and to Z, is parallel to the c crystal axis.<ref name=Dana/><ref name=HOM/>  The [[Refractive index|refractive indices]] are close to n<sub>α</sub> = 1.52, n<sub>β</sub> = 1.66, n<sub>γ</sub> = 1.67, with different sources quoting slightly different values: 
*n<sub>α</sub> = 1.520, n<sub>β</sub> = 1.667, n<sub>γ</sub> =  1.669<ref name=Dana/>
*n<sub>α</sub> = 1.516 – 1.520, n<sub>β</sub> = 1.664 – 1.667, n<sub>γ</sub> = 1.666 – 1.668<ref name=Mindat/><ref name=Webmin/>
*n<sub>α</sub>  = 1.517, n<sub>β</sub> = 1.663, n<sub>γ</sub> = 1.667 (synthetic material)<ref name=AM61>Speer, J A and Hensley-Dunn, M L (1976) Strontianite composition and physical properties.  American Mineralogist 61:1001–1004</ref>
The maximum [[birefringence]] δ is 0.15<ref name=Mindat/> and the measured value of [[Conoscopic interference pattern|2V]] is 7°, calculated 12° to 8°.<ref name=Mindat/><ref name=Webmin/>

If the colour of the incident light is changed, then the refractive indices are modified, and the value of 2V changes. This is known as dispersion of the optic axes. For strontianite the effect is weak, with 2V larger for violet light than for red light r < v.<ref name=HOM/>

== Luminescence ==

Strontianite is almost always [[Fluorescence|fluorescent]].<ref name=Mindat/>  It fluoresces bright yellowish white under shortwave, mediumwave and longwave [[ultraviolet]] radiation.  If the luminescence persists after the ultraviolet source is switched off the sample is said to be [[Phosphorescence|phosphorescent]].  Most strontianite phosphoresces a strong, medium duration, yellowish white after exposure to all three wavelengths.<ref name=MinRec37>The Mineralogical Record (2006)  37-1:44</ref>  It is also fluorescent and phosphorescent in [[X-rays]] and [[Cathode ray|electron beams]].  All materials will glow red hot if they are heated to a high enough temperature (provided they do not decompose first); some materials become luminescent at much lower temperatures, and this is known as [[thermoluminescence]].  Strontianite is sometimes thermoluminescent.<ref name=Dana/><ref name=Mindat/><ref name=HOM/>

== Physical properties ==
[[Cleavage (crystal)|Cleavage]] is nearly perfect parallel to one set of prism faces, [[Miller index|{110}]], and poor on {021}.  Traces of cleavage have been observed on {010}.<ref name=Mindat/><ref name=HOM/>
 
[[Crystal twinning|Twinning]] is very common, with twin plane {110}.  The twins are usually contact twins; in a contact twin the two individuals appear to be reflections of each other in the twin plane.  Penetration twins of strontainite are rarer; penetration twins are made up of interpenetrating individuals that are related to each other by rotation about a twin axis.  Repeated twins are made up of three or more individuals twinned according to the same law.  If all the twin planes are parallel then the twin is polysynthetic, otherwise it is cyclic.<ref name=MOM/>  In strontianite repeated twinning forms cyclic twins with three or four individuals, or polysynthetic twins.<ref name=Dana/><ref name=Mindat/><ref name=HOM/>

The mineral is brittle, and breaks with a subconchoidal to uneven [[Fracture (geology)|fracture]].  It is quite soft, with a [[Mohs hardness]] of {{frac|3|1|2}},<ref name=Mindat/> between [[calcite]] and [[fluorite]].  The [[specific gravity]] of the pure [[endmember]] with no calcium substituting for strontium is 3.78,<ref name=AM61/> but most samples contain some calcium, which is lighter than strontium, giving a lower specific gravity, in the range 3.74 to 3.78.<ref name=Mindat/>  Substitutions of the heavier ions [[barium]] and/or [[lead]] increase the specific gravity, although such substitutions are never very abundant.<ref name=AM61/>  Strontianite is soluble in dilute [[hydrochloric acid]] HCl<ref name=Dana/><ref name=Mindat/> and it is not [[Radioactive decay|radioactive]].<ref name=Webmin/>

== Environment and associations ==
Strontianite is an uncommon low-temperature [[hydrothermal]] mineral formed in [[Vein (geology)|veins]] in [[limestone]], [[marl]], and [[chalk]], and in [[geode]]s and [[concretions]].  It occurs rarely in hydrothermal metallic veins but is common in [[carbonatite]]s.<ref name=HOM/>  It most likely crystallises at or near 100&nbsp;°C.  Its occurrence in open [[vug]]s and veins suggests crystallisation at very low pressures, probably at most equal to the [[Fluid statics#Hydrostatic pressure|hydrostatic pressure]] of the [[ground water]].<ref name=AM61/>  Under appropriate conditions it alters to [[Celestine (mineral)|celestine]] SrSO<sub>4</sub>, and it is itself found as an alteration from celestine.<ref name=Dana/>  These two minerals are often found in association, together with [[baryte]], [[calcite]], [[harmotome]] and [[sulfur]].<ref name=HOM/>

== Occurrences ==

=== Type locality ===
The [[Type locality (geology)|type locality]] is [[Strontian]], North West Highlands ([[Argyllshire]]), [[Scotland]], UK.  The [[Type specimen (mineralogy)|type material]] occurred in [[Hydrothermal vein|veins]] in [[gneiss]].<ref name=Dana/>

Other UK localities include Brownley Hill Mine (Bloomsberry Horse Level), Nenthead, [[Alston Moor]] District, North Pennines, North and Western Region (Cumberland), Cumbria, England, associated with a suite of primary minerals ([[bournonite]], [[millerite]] and [[ullmannite]]) which are not common in other [[Carbonate hosted lead zinc ore deposits|Mississippi Valley-type deposits]].<ref name=MinRec41>The Mineralogical Record (2010)  41-1:62 supplement</ref>

=== Canada ===
The Francon quarry, [[Montréal]], Québec.  <br />
Strontianite is very common at the Francon Quarry, in a great variety of habits.  It is a late stage mineral, sometimes found as multiple generations.  It is found as translucent to opaque, white to pale yellow or beige generally smooth surfaced spheroids, hemispheres and compact spherical and botryoidal [[Aggregate (geology)|aggregate]]s to 10&nbsp;cm in diameter, and as spheres consisting of numerous radiating acicular crystals, up to 1&nbsp;cm across.  Also as tufts, parallel bundles, and sheaf-like clusters of fibrous to acicular crystals, and as white, finely granular porcelaneous and waxy globular aggregates.  Transparent, pale pink, columnar to tabular sixling twins up to 1&nbsp;cm in diameter have been found, and aggregates of stacked stellate sixling twins consisting of transparent, pale yellow tabular crystals.<ref name=MinRec37/>

Another Canadian occurrence is at [[Nepean, Ontario|Nepean]], Ontario, in vein deposits in [[limestone]].<ref name=Dana/>

=== Germany ===
Commercially important deposits occur in [[marls]] in [[Westphalia]],<ref name=Dana/> and it is also found with [[zeolites]] at Oberschaffhausen, [[Bötzingen]], Kaiserstuhl, Baden-Württemberg.<ref name=Dana/>

=== India ===
In [[Trichy]] (Tiruchirappalli; Tiruchi), Tiruchirapalli District, Tamil Nadu, it occurs with [[Celestine (mineral)|celestine]] SrSO<sub>4</sub>, [[gypsum]] and [[phosphate nodule]]s in [[clay]].<ref name=Dana/>

=== Mexico ===
It occurs in the [[Sierra Mojada]] District, with [[Celestine (mineral)|celestine]] in a [[lead]]-[[silver]] deposit.<ref name=Dana/>

=== Russia ===
It occurs in the Kirovskii [[apatite]] mine<!-- (also spelled Kirovsky Mine; Kirovskii Mine; Kirov Mine) -->, Kukisvumchorr Mt, [[Khibiny Massif]], [[Kola Peninsula]], Murmanskaja Oblast', Northern Region, in late hydrothermal assemblages in cavities in [[pegmatites]], associated with [[kukharenkoite-(La)]], [[microcline]], [[albite]], [[calcite]], [[nenadkevichite]], [[hilairite]], [[catapleiite]], [[donnayite-(Y)]], [[synchysite-(Ce)]], [[pyrite]] and others.<ref name=MinRec35C>The Mineralogical Record (2004) 35-4:355</ref>

It also occurs at [[Yukspor]] Mountain, Khibiny Massif, Kola Peninsula, Murmanskaja Oblast', Northern Region, in an [[aegerine]]-[[natrolite]]-[[microcline]] vein in [[foyaite]], associated with [[aegirine]], [[anatase]], [[ancylite-(Ce)]], [[barylite]], [[catapleiite]], [[cerite-(Ce)]], [[cerite-(La)]], [[chabazite-(Ca)]], [[edingtonite]], [[fluorapatite]], [[galena]], [[ilmenite]], [[microcline]], [[natrolite]], [[sphalerite]] and [[vanadinite]].<ref name=MinRec35A>The Mineralogical Record (2004) 35-2:176</ref>  At the same locality it was found in [[alkaline]] [[pegmatite]] veins associated with [[clinobarylite]], [[natrolite]], [[aegirine]], [[microcline]], [[catapleiite]], [[fluorapatite]], [[titanite]], [[fluorite]], [[galena]], [[sphalerite]], [[annite]], [[astrophyllite]], [[lorenzenite]], [[labuntsovite-Mn]], [[kuzmenkoite-Mn]], [[cerite-(Ce)]], [[edingtonite]], [[ilmenite]] and [[calcite]].<ref name=MinRec35B>The Mineralogical Record 35-4:347 (2004)</ref>

=== United States ===
In the [[Gulf coast]] of [[Louisiana]] and [[Texas]], strontianite occurs with [[Celestine (mineral)|celestine]] in [[calcite]] [[cap rock]] of [[salt domes]].<ref name=Dana/>

At the Minerva Number 1 Mine (Ozark-Mahoning Number 1 Mine) Ozark-Mahoning Group, [[Cave-in-Rock, Illinois]], in the Kentucky [[Fluorspar]] District, [[Hardin County, Kentucky|Hardin County]] strontanite occurs as white, brown or rarely pink tufts and bowties of acicular crystals with slightly curved terminations.<ref name=R&M85>Rocks & Minerals (2010) 85-3:212</ref>

In the [[Silurian]] [[Lockport (town), New York|Lockport]] Group, Central and Western [[New York (state)|New York]]  strontianite is observed in cavities in eastern Lockport, where it occurs as small white radiating sprays of acicular crystals.<ref name=R&M84>Rocks & Minerals (2009) 84-4:332</ref>

In [[Schoharie County]], New York, it occurs in [[geode]]s and [[Hydrothermal vein|veins]] with [[Celestine (mineral)|celestine]] and [[calcite]] in [[limestone]],<ref name=Dana/> and in [[Mifflin County]], Pennsylvania, it occurs with [[aragonite]], again in [[limestone]].<ref name=Dana/>

<gallery mode="packed" heights="120">
Strontianite-118172.jpg|Strontianite from Strontian, Scotland
Dresserite-Strontianite-lor03a.jpg|[[Dresserite]] and Strontianite from the Francon quarry, Canada
Strontianite-Baryte-160390.jpg|Strontianite from the Dreislar Mine, North Rhine-Westphalia, Germany
Strontianite-170614.jpg|Strontianite from Texas, US
Strontianite-208781.jpg|Strontianite from Illinois, US
Strontianite Strontium carbonate Barstow San Bernardino County California 1845.jpg|Strontianite from California
</gallery>

== See also ==
* [[Strontian process]]

==References==
{{reflist}}

== External links ==
{{commons category-inline}}
* [http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=00234 JMol]

{{Authority control}}

[[Category:Lochaber]]
[[Category:Strontium minerals]]
[[Category:Carbonate minerals]]
[[Category:Aragonite group]]
[[Category:Orthorhombic minerals]]
[[Category:Minerals in space group 62]]
[[Category:Luminescent minerals]]
[[Category:Geology of Scotland]]
[[Category:Minerals described in 1791]]