Talmessite
Talmessite
Talmesite | |
---|---|
General | |
Category | Arsenate mineral |
Formula (repeating unit) | Ca2Mg(AsO4)2.2H2O |
Strunz classification | 7/C.17-50 or 8.CG.05 |
Dana classification | 40.02.02.05 |
Crystal system | Triclinic B1, space group PB1 (All) Triclinic (AM45) |
Identification | |
Formula mass | 418.33 g (Webmin) |
Color | White, colourless, pale green (nickelian), brownish, pink or brownish pink (cobaltian); colourless in transmitted light (All). Colourless (AM42) Pale green (AM45) |
Crystal habit | As crystals, to 3 mm; radiating fibrous aggregates, may be stalactitic or in crusts (HOM). Fine crystalline aggregates (Dana) Prismatic (AM42) |
Twinning | Polysynthetic twinning (AM42) |
Mohs scale hardness | 5 (All) |
Luster | Vitreous (Mindat, Webmin, HOM) |
Streak | white (Webmin) |
Diaphaneity | Transparent to Translucent (All) |
Specific gravity | 3.57 (Dana), 3.421 (HOM), 3.421 (AM45) cobaltoan 3.574 (AM45) 3.2 – 3.5 (AM50) |
Optical properties | Biaxial (–) (AM45, All) positive (AM42) |
Refractive index | nα = 1.672, nβ = 1.685, nγ = 1.698 (am50, All) nα = 1.680, cobaltoan 1.695, nγ = 1.69, cobaltoan 1.73 (AM45) |
Birefringence | δ = 0.026 (Mindat, Webmin) |
Pleochroism | Cobaltoan variety is pleochroic colourless to pale rose (AM45) |
Other characteristics | Not radioactive (Webmin). Loss of H2O at 450 deg (AM45) |
References | [1] [2] [3] [4] [5] [6] [7] [8] |
Dana: 40 hydrated normal phosphates, arsenates and vanadatesNamed in 1960 for the locality (Dana)
Varieties: Cobaltoan Talmessite, Nickeloan Talmessite (Mindat)
Fairfieldite group. Forms a series with gaitite (Mindat, HOM), β-Roselite (Mindat)
Fairfieldite Group (Dana, Mindat, HOM)
Dimorphic with wendwilsonite (Dana)
Fairfieldite Group Members: (Mindat)
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
Formula: Ca2Mg(AsO4)2.2H2O (IMA) Crystal Class: Triclinic B1, space group PB1 (All) Triclinic (AM45) Structure: The structure is dominated by chains of tetrahedral AsO4 and octahedral [(cation-O4(H2O)2)] that parallel the c axis. The B octahedral are compressed, resulting in chain disorder (Dana) Unit Cell Parameters: Z = 1 (Dana, Webmin, HOM) a = 5.874 Å, b = 6.943 Å, c = 5.537 Å, α = 97.3°, β = 108.7°, γ = 108.1° (Dana) a = 5.87Å, b = 6.94Å, c = 5.53Å α = 97.3°, β = 108.7°, γ = 108.1° (Mindat) a = 5.89, b = 7.69, c = 5.56, alpha = 112.633°, beta = 70.817°, gamma = 119.417° (AM45, AM50, Webmin) a = 5.874(7), b = 6.943(11), c = 5.537(6), α = 97.3(1)◦ β = 108.7(1)◦ γ = 108.1(2)◦ (HOM) Calculated specific gravity = 3.42 (Dana), 3.63 (Webmin), 3.53 (HOM), 3.491 (AM45) 3.49 (AM50)
Appearance
Crystal habits: As crystals, to 3 mm; radiating fibrous aggregates, may be stalactitic or in crusts (HOM). Fine crystalline aggregates (Dana) Prismatic (AM42) Colour: White, colourless, pale green (nickelian), brownish, pink or brownish pink (cobaltian); colourless in transmitted light (All). Colourless (AM42) Pale green (AM45) Streak: white (Webmin) Lustre: Vitreous (Mindat, Webmin, HOM) Diaphaneity: Transparent to Translucent (All)
Physical properties
Molar Mass : 418.33 gm (Webmin) Polysynthetic twinning (AM42) Hardness: 5 (All) Specific Gravity: 3.57 (Dana), 3.421 (HOM), 3.421 (AM45) cobaltoan 3.574 (AM45) 3.2 – 3.5 (AM50) Other Characteristics: Not radioactive (Webmin). Loss of H2O at 450 deg (AM45)
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
Occurrence and Associations: A rare secondary species formed typically in the oxidized zone of some hydrothermal mineral deposits, an alteration product of realgar, orpiment, or Cu–Ni arsenides (Webmin, HOM). Zone of alteration of cobalt arsenide deposits (AM42) Zone of oxidation (AM45) Association: Gaitite, erythrite, annabergite, picropharmacolite, pharmacolite, austinite, fluorite, barite, aragonite, calcite, dolomite (HOM). Associated with aragonite and dolomite at the type locality (AM45) Associated with dolomite at the type locality (Dana).
Localities
Type Locality Talmessi Mine (Talmesi Mine; Telmessi Mine; Telmesi Mine), Anarak District, Nain County (Nayin County), Esfahan Province (Isfahan Province; Aspadana Province), Iran (Mindat) Type Material: National School of Mines, Paris, France; the Natural History Museum, London, England (HOM).
Synonyms (Mindat): Arsenate-belovite, Belovite (of Nefedov) Name in Other Languages: German:Arsenatbelowit, Talmessit Russian:Талмессит Spanish:Talmessita
References
- ^ <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>
- ^ 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>
- ^ <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>
- ^ <Gaines et al (1997) Dana’s New Mineralogy, Eighth Edition. Wiley>
- ^ <http://www.mindat.org/min-3876.html>
- ^ <http://www.webmineral.com/data/Talmessite.shtml#.VN2Jzi6kFjo>
- ^ <http://www.handbookofmineralogy.org>
- ^ http://pubsites.uws.edu.au/ima-cnmnc/>