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Macphersonite

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Macphersonite
General
CategoryCarbonate mineral
Formula
(repeating unit)
Pb4(SO4)(CO3)2 (OH)2
IMA symbolMps[1]
Strunz classification5.BF.40
Dana classification17.01.04.01
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPcab
Unit cella = 10.37 Å, b = 23.10 Å,
c = 9.25 Å,
β = 106.43°; Z = 8
Identification
Formula mass1,078.90 g/mol
ColorWhite, pale amber, colorless
Crystal habitPseudo hexagonal, tabular
TwinningPolysynthetic, lamellar, contact
CleavagePerfect on {010}
FractureUneven
Mohs scale hardness2.5 - 3
LusterAdamantine, otherwise resinous
StreakWhite
Specific gravity6.50
Optical propertiesBiaxial (-)
Refractive indexnα = 1.870 nβ = 2.000 nγ = 2.010
Birefringenceδ = 0.140
2V angle35-36°
Dispersionr > v
Ultraviolet fluorescenceA very strong and vivid yellow
Other characteristicsPolymorph of leadhillite and susannite
References[2][3][4][5][6]

Macphersonite, Pb4(SO4)(CO3)2 (OH)2, is a carbonate mineral that is trimorphous with leadhillite and susannite. Macphersonite is generally white, colorless, or a pale amber in color and has a white streak. It crystallizes in the orthorhombic system with a space group of Pcab. It is fairly soft mineral that has a high specific gravity.

Macphersonite is named after Harry Gordon Macpherson,[4] a keeper of minerals at the Royal Scottish Museum. It was discovered and accepted in 1984.

Structure

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The structure of macphersonite is represented as a sequence of three layers stacked along the [001]. The first layer is a sulfate tetrahedra, the second is of lead and hydroxide, and the third is a layer composed of lead and carbonate. Stacking of the three layers can be detailed as ...BABCCBABCC...[5] similar to leadhillite. Two C layers of lead carbonate in the BAB stacking provide a weak connection that leads to the perfect {001} cleavage.

Physical properties

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The Leadhills macphersonite is a very pale amber to colorless in color, while the Argentolle mine macphersonite is colorless to white.[4] It has a luster of adamantine on fresh surfaces and elsewhere it is resinous. Macphersonite is soft with a 2.5-3 on the Mohs hardness, has an uneven fracture with a high density of 6.5g/cm3.[3]

Macphersonite has a very strong yellow fluorescence under both long and short wave, ultraviolet is displayed by the Leadhills specimens, the Argentolle material does not fluoresce.

Occurrence

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Macphersonite is found in the Leadhills region of southwest Scotland and in the Saint-Prix, Saône-et-Loire region of France. It is the rarest of the three polymorphs. It occurs in lead deposits associated with cerussite, susannite, caledonite, scotlandite, leadhillite, galena and pyromorphite.

References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ a b Web Mineral
  4. ^ a b c Livingstone, A.; Sarp, H. (1984). "Macphersonite, a new mineral from Leadhills, Scotland, and Saint-Prix, France – a polymorph of leadhillite and susannite" (PDF). Mineralogical Magazine. 48 (347): 277–82. Bibcode:1984MinM...48..277L. doi:10.1180/minmag.1984.048.347.14. S2CID 55488942. Retrieved 26 June 2016.
  5. ^ a b Steele, Ian, Pluth, Joseph, Livingstone, Alan. Crystal structure of macphersonite (Pb4(SO4)(CO3)2 (OH)2): comparison with leadhillite Mineralogical Magazine, 1998 vol 62(4), pp 451=459
  6. ^ Macphersonite data on Mindat