Macphersonite

Macphersonite
General
Category Carbonate mineral
Formula
(repeating unit)		 Pb4(SO4)(CO3)2 (OH)2
Strunz classification 5.BF.40
Dana classification 17.01.04.01
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pcab
Unit cell a = 10.37 Å, b = 23.10 Å,
c = 9.25 Å,
β = 106.43°; Z = 8
Identification
Formula mass 1,078.90 g/mol
Color White, pale amber, colorless
Crystal habit Pseudo hexagonal, tabular
Twinning Polysynthetic, lamellar, contact
Cleavage Perfect on {010}
Fracture Uneven
Mohs scale hardness 2.5 - 3
Luster Adamantine, otherwise resinous
Streak White
Specific gravity 6.50
Optical properties Biaxial (-)
Refractive index nα = 1.870 nβ = 2.000 nγ = 2.010
Birefringence δ = 0.140
2V angle 35-36°
Dispersion r > v
Ultraviolet fluorescence A very strong and vivid yellow
Other characteristics Polymorph of leadhillite and susannite
References [1][2][3][4][5]

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,[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 coloroless 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.

References

  1. ↑ Mineralienatlas
  2. 1 2 Web Mineral
  3. 1 2 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. 1 2 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
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.