Crystal structure of susannite, Pb4SO4(CO3)2(OH)2: a trimorph with macphersonite and leadhillite
Steele, Ian M.; Pluth, Joseph J.; Livingstone, Alec
European Journal of Mineralogy Volume 11 Number 3 (1999), p. 493 - 500
published: May 25, 1999
manuscript accepted: Dec 18, 1998
manuscript received: Jan 5, 1998
ArtNo. ESP147051103008, Price: 29.00 €
Abstract The crystal structure of susannite (Pb4SO4(CO3)2(OH)2, P3, a = 9.0718(7), c = 11.570(1) Å) from Leadhills, Scotland has been determined to R = 0.053. Susannite is trimorphous with macphersonite and leadhillite and is composed of SO4 (= A), Pb (= B) and Pb-CO3 (= C) layers. The stacking sequence of these layers along  is .. ABCCBABCCB... and is the same sequence found in the other trimorphs. The two C layers are equivalent to a slab of cerussite. The clear difference among the trimorphs is the relative orientation of SO4 tetrahedra within layer A. For susannite, a row of tetrahedra along a* shows the up (U) or down (D) pointing sequence ..UUDUUD... This contrasts with leadhillite which shows ..DDUUDDUU.. and macphersonite which shows ..UDUDUD.. sequences. The reversible phase transformation between leadhillite and susannite at about 80 °C requires an apparent rotation of two SO4 groups within four unit cells of susannite. This sulfate rearrangement requires only minor adjustments of Pb polyhedra within the B layer. The double C-C layer forms a common backbone of these trimorphs.