Macphersonite
| Macphersonite | |
|---|---|
 | |
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | Pb4(SO4)(CO3)2 (OH)2 |
| IMA symbol | Mps[1] |
| 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 | [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
[edit]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
[edit]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
[edit]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
[edit]- ^ 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.
- ^ Mineralienatlas
- ^ a b Web Mineral
- ^ 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.
- ^ 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
- ^ Macphersonite data on Mindat