Macphersonite

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
General
CategoryCarbonate mineral
Formula
(repeating unit)		Pb4(SO4)(CO3)2 (OH)2
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[1][2][3][4][5]

Macphersonite is named after Harry Gordon Macpherson,[3] a keeper of minerals at the Royal Scottish Museum. It was discovered and accepted in 1984.

Structure

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...[4] 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

The Leadhills macphersonite is a very pale amber to colorless in color, while the Argentolle mine macphersonite is colorless to white.[3] 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.[2]

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

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.

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References
  1. Mineralienatlas
  2. Web Mineral
  3. 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: 277–82. doi:10.1180/minmag.1984.048.347.14. Retrieved 26 June 2016.
  4. 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
  5. Macphersonite data on Mindat
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