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| strunz = 7/C.17-50 or 8.CG.05
| strunz = 7/C.17-50 or 8.CG.05
| dana = 40.02.02.05
| dana = 40.02.02.05
| color = White or colourless. Nickeloan talmessite is pale green and cobaltoan is brownish or pink. Colourless in transmitted light.
| color = White or colourless, pale green (nickel-rich) or brownish or pink (cobalt-rich). Colourless in transmitted light.
| habit = Prismatic crystals<ref name=AM42/>, radiating fibrous aggregates<ref name=HOM/>
| habit = Prismatic crystals<ref name=AM42/>, radiating fibrous aggregates<ref name=HOM/>
| system = Triclinic {{overline|1}}, space group P{{overline|1}}
| system = Triclinic {{overline|1}}, space group P{{overline|1}}
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== Appearance ==
== Appearance ==
Talmessite occurs as prismatic crystals to 3 mm<ref name=AM42/>, as radiating fibrous aggregates<ref name=HOM/> or as fine crystalline aggregates<ref name=Dana/>; it may also be stalactitic or in crusts.<ref name=HOM/>. Pure talmessite is white or colourless, and colourless in transmitted light, but nickeloan varieties are pale green<ref name=AM45/> and cobaltoan varieties may be brownish, pink or the purple colour typical of many cobalt minerals. The [[Streak (mineralogy)|streak]] is white<ref name=Webmin/> and crystals are transparent to translucent with a [[vitreous lustre]].
Talmessite occurs as [[prism|prismatic]] crystals to 3 mm<ref name=AM42/>, as radiating fibrous aggregates<ref name=HOM/> or as fine crystalline aggregates<ref name=Dana/>; it may also be [[Stalactite|stalactitic]] or in crusts.<ref name=HOM/>. Pure talmessite is white or colourless, and colourless in [[transmitted light]], but [[nickel]]-rich varieties are pale green<ref name=AM45/> and [[cobalt]]-rich varieties may be brownish, pink or the purple colour typical of many cobalt minerals. The [[Streak (mineralogy)|streak]] is white<ref name=Webmin/> and crystals are transparent to translucent with a [[vitreous lustre]].


== Physical properties ==
== Physical properties ==
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== Occurrence ==
== Occurrence ==
Talmessite is a rare [[secondary mineral]] formed typically in the [[oxidized zone]] of some [[hydrothermal mineral deposits]], as an alteration product of [[realgar]], [[orpiment]], or Cu–Ni [[arsenides]].<ref name=Webmin/> <ref name=HOM/> Cobaltoan varieties are found in the [[zone of alteration]] of [[cobalt arsenide deposits]].<ref name=AM42/> It occurs associated with [[gaitite]], [[erythrite]], [[annabergite]], [[picropharmacolite]], [[pharmacolite]], [[austinite]], [[fluorite]], [[baryte]], [[aragonite]], [[calcite]] and [[dolomite]].<ref name=HOM/> At the [[type locality]] it is associated with [[aragonite]] and [[dolomite]]. <ref name=AM45/>
Talmessite is a rare [[Supergene (geology)#Oxidized zone|secondary mineral]] formed typically in the oxidized zone of some [[Ore genesis#Hydrothermal processes|hydrothermal]] mineral deposits, as an alteration product of [[realgar]], [[orpiment]], or Cu–Ni [[Arsenide|arsenides]].<ref name=Webmin/> <ref name=HOM/> [[Cobalt]]-rich varieties are found in the oxidised zone of cobalt arsenide deposits.<ref name=AM42/> It occurs associated with [[gaitite]], [[erythrite]], [[annabergite]], [[picropharmacolite]], [[pharmacolite]], [[austinite]], [[fluorite]], [[baryte]], [[aragonite]], [[calcite]] and [[dolomite]].<ref name=HOM/> At the [[type locality]] it is associated with [[aragonite]] and [[dolomite]]. <ref name=AM45/>


== Localities ==
== Localities ==
The [[type locality]] is the Talmessi Mine, [[Anarak]] District, Nain County, Esfahan Province, Iran,<ref name=Mindat/> and [[type material is conserved at the [[National School of Mines, Paris]], France and at the [[Natural History Museum, London]], England.<ref name=HOM/>
The [[Type locality (geology)|type locality]] is the Talmessi Mine, [[Anarak]] District, Nain County, Esfahan Province, Iran,<ref name=Mindat/> and [[type material]] is conserved at the [[National School of Mines, Paris]], France and at the [[Natural History Museum, London]], England.<ref name=HOM/>




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== References ==
== References ==

<!--- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes on how to create references using <ref></ref> tags, these references will then appear here automatically -->
{{Reflist}}
{{Reflist}}


Revision as of 06:00, 25 February 2015


Talmessite

Talmesite
Talmessite from Gold Hill Mine, Utah, USA
General
CategoryArsenate mineral
Formula
(repeating unit)		Ca2Mg(AsO4)2.2H2O
Strunz classification7/C.17-50 or 8.CG.05
Dana classification40.02.02.05
Crystal systemTriclinic 1, space group P1
Identification
Formula mass418.33 g[1]
ColorWhite or colourless, pale green (nickel-rich) or brownish or pink (cobalt-rich). Colourless in transmitted light.
Crystal habitPrismatic crystals[2], radiating fibrous aggregates[3]
TwinningPolysynthetic[2]
Mohs scale hardness5
LusterVitreous
StreakWhite[1]
DiaphaneityTransparent to translucent
Specific gravity3.421[4] [3], cobaltoan varieties 3.574[4]
Optical propertiesBiaxial (–)
Refractive indexnα = 1.672, nβ = 1.685, nγ = 1.698
Birefringenceδ = 0.026
PleochroismThe cobaltoan variety is pleochroic, colourless to pale rose[4]
Other characteristicsNot radioactive.[1] It loses water of crystallisation at 450o[4]
References[2] [4] [5] [6] [7] [1] [3] [8]

Talmessite is a hydrated calcium magnesium arsenate, often with significant amounts of cobalt or nickel.[7] It was named in 1960 for the type locality, the Talmessi mine, Anarak district, Iran. It forms a series with β-Roselite, where cobalt replaces some of the magnesium, and with gaitite, where zinc replaces the magnesium.[7] [3] All these minerals are members of the fairfieldite group. Talmessite is dimorphic with wendwilsonite (which is not a member of this group).[6]

Members of the fairfieldite group[7]

Cassidyite Ca2(Ni2+,Mg)(PO4)2 · 2H2O

Collinsite Ca2(Mg,Fe2+)(PO4)2 · 2H2O

Fairfieldite Ca2(Mn2+,Fe2+)(PO4)2 · 2H2O

Gaitite Ca2Zn(AsO4)2 · 2H2O

Messelite Ca2(Fe2+,Mn2+)(PO4)2 · 2H2O

Nickeltalmessite Ca2Ni(AsO4)2 · 2H2O

Parabrandtite Ca2Mn2+(AsO4)2 · 2H2O

Unnamed (Fe2+-analogue of Parabrandtite) Ca2Fe2+(AsO4)2 · 2H2O

β-Roselite Ca2(Co2+,Mg)(AsO4)2 · 2H2O

Talmessite Ca2Mg(AsO4)2.2H2O

Crystallography

The formula for talmessite is Ca2Mg(AsO4)2.2H2O[8]. It is a triclinic mineral[4], crystal class 1, space group P1. There is one formula unit per unit cell (Z = 1) and the unit cell parameters are variously given as a = 5.87Å, b = 6.94Å, c = 5.53Å α = 97.3°, β = 108.7°, γ = 108.1°[6] [7] [3], or a = 5.89, b = 7.69, c = 5.56, alpha = 112.633°, beta = 70.817°, gamma = 119.417°,[4] [5] [1]. These values give a calculated specific gravity varying from 3.42 to 3.63.
The structure is dominated by chains of tetrahedral AsO4 and octahedral [(cation-O4(H2O)2)] groups that parallel the c crystal axis. The octahedral are compressed, resulting in chain disorder[6]

Appearance

Talmessite occurs as prismatic crystals to 3 mm[2], as radiating fibrous aggregates[3] or as fine crystalline aggregates[6]; it may also be stalactitic or in crusts.[3]. Pure talmessite is white or colourless, and colourless in transmitted light, but nickel-rich varieties are pale green[4] and cobalt-rich varieties may be brownish, pink or the purple colour typical of many cobalt minerals. The streak is white[1] and crystals are transparent to translucent with a vitreous lustre.

Physical properties

Talmessite is a moderately hard mineral, with Mohs hardness 5, harder than fluorite but not as hard as quartz. The specific gravity calculated from the formula and the cell dimensions is 3.49,[9] [5] but the measured value is less for ordinary talmessite, at 3.42[4] [3] and more for the cobaltoan variety, at 3.57.[4] [6] The mineral displays polysynthetic twinning.[2] It is not radioactive[1] and it loses water of crystallisation at 450o.[4]

Optical properties

Optic Class: Biaxial (–) (AM45, All) positive (AM42) Refractive Indices: nα = 1.672, nβ = 1.685, nγ = 1.698 (am50, All) nα = 1.680, cobaltoan 1.695, nγ = 1.69, cobaltoan 1.73 (AM45) Maximum birefringence δ = 0.026 (Mindat, Webmin) 2V measured = ~90o (AM50, All), 2V calculated = 88° (Mindat, Webmin) Dispersion of the optic axes: r > v strong (Mindat) Cobaltoan variety is pleochroic colourless to pale rose (AM45)

Occurrence

Talmessite is a rare secondary mineral formed typically in the oxidized zone of some hydrothermal mineral deposits, as an alteration product of realgar, orpiment, or Cu–Ni arsenides.[1] [3] Cobalt-rich varieties are found in the oxidised zone of cobalt arsenide deposits.[2] It occurs associated with gaitite, erythrite, annabergite, picropharmacolite, pharmacolite, austinite, fluorite, baryte, aragonite, calcite and dolomite.[3] At the type locality it is associated with aragonite and dolomite. [4]

Localities

The type locality is the Talmessi Mine, Anarak District, Nain County, Esfahan Province, Iran,[7] and type material is conserved at the National School of Mines, Paris, France and at the Natural History Museum, London, England.[3]



References

  1. ^ a b c d e f g h http://www.webmineral.com/data/Talmessite.shtml#.VN2Jzi6kFjo
  2. ^ a b c d e f American Mineralogist (1957) 42:583 abstract from Yakhontova, L K and G A Sidorenko (1956) A new mineral – arsenate-belovite. Zapiski V ses Mineralog Obshch 85 No 3, 297-302
  3. ^ a b c d e f g h i j k http://www.handbookofmineralogy.org
  4. ^ a b c d e f g h i j k l American Mineralogist (1960) 45:1315 abstract from Bariand, P. & Herpin, P. (1960): Un arséniate de calcium et de magnésium, isomorphe de la β rosélite. Bulletin de la Société française de Minéralogie et de Cristallographie: 83: 118-121>
  5. ^ a b c American Mineralogist (1965) 50:813 abstract from Pierrot, R. (1964): Contribution à la minéralogie des arséniates calciques et calcomagnésiens naturels. Bull. Soc. fr. Minéral. Cristallogr. 87, 169-211
  6. ^ a b c d e f Gaines et al (1997) Dana’s New Mineralogy, Eighth Edition. Wiley
  7. ^ a b c d e f http://www.mindat.org/min-3876.html
  8. ^ a b http://pubsites.uws.edu.au/ima-cnmnc/>
  9. ^ Cite error: The named reference AM49 was invoked but never defined (see the help page).
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