Chloroxiphite Pb 3 CuO 2 (OH) 2 Cl 2 : structure refinement and description in terms of oxocentred OPb 4 tetrahedra

The new mineral somersetite, has been found at Torr Works (‘Merehead quarry’) in Somerset, England, United Kingdom. Somersetite is green or white (typically it is similar visually to hydrocerussite-like minerals but with a mint-green tint), forms plates and subhedral grains up to 5 mm across and up to 2 mm thick. In bi-coloured crystals it forms very thin intergrowths with plumbonacrite. The empirical formula of somersetite is Pb8.00C5.00H4.00O20. The simplified formula is Pb8O(OH)4(CO3)5, which requires: PbO = 87.46, CO2 = 10.78, H2O = 1.76, total 100.00 wt.%.The infrared spectrum of somersetite is similar to that of plumbonacrite and, to a lesser degree, hydrocerussite. Somersetite is hexagonal, P63/mmc, a = 5.2427(7), c = 40.624(6) Å, V = 967.0(3) Å3 and Z = 2. The eight strongest reflections of the powder X-ray diffraction (XRD) pattern [d,Å(I)(hkl)] are: 4.308(33)(103), 4.148(25)(104), 3.581(40)(107), 3.390(100)(108), 3.206(55)(109), 2.625(78)(110), 2.544(98)(0.0.16) and 2.119(27)(1.0.17). The crystal structure was solved from single-crystal XRD data giving R1 = 0.031. The structure of somersetite is unique and consists of the alternation of the electroneutral plumbonacrite-type [Pb5O(OH)2(CO3)3]0 and hydrocerussite-type [Pb3(OH)2(CO3)2]0 blocks separated by stereochemically active lone electron pairs on Pb2+. There are two blocks of each type per unit cell in the structure, which corresponds to the formula [Pb5O(OH)2(CO3)3][Pb3(OH)2(CO3)2] or Pb8O(OH)4(CO3)5 in a simplified representation. The 2D blocks are held together by weak Pb–O bonds and weak interactions between lone pairs.

Section: Discussionmentioning

confidence: 99%

Somersetite, Pb₈O(OH)₄(CO₃)₅, a new complex hydrocerussite-related mineral from the Mendip Hills, England

Siidra

Nekrasova

Turner³

et al. 2018

“…FOR some time, the authors have been investigating the mineralogy of the Mendip Hills with particular reference to the assemblages of Pb oxychlorides and other Pb secondary minerals contained within the manganese pods that occur there, as well as similar oxychloride occurrences elsewhere in the world including Långban in Sweden, the Kombat mine in Namibia, the Mammoth St. Antony mine in Tiger, Arizona and the Kunibert mine in Rhine-Westphalia (see e.g. Turner, 2006;Rumsey 2008;Siidra et al 2008;Krivovichev et al 2009;Turner and Rumsey, 2010;Rumsey et al 2011;Turner et al 2012a;Williams et al, 2012, Siidra et al, 2013a.…”

Section: Introductionmentioning

confidence: 99%

“…The most abundant oxychloride mineral in the assemblage is mendipite Pb 3 Cl 2 O 2 (Spencer, 1923). Chloroxiphite Pb 3 CuO 2 (OH) 2 Cl 2 (Siidra et al, 2008), diaboleite Pb 2 Cu(OH) 4 Cl 4 (Cooper and Hawthorne, 1995) and paralaurionite Pb(OH)Cl occur in, and often entirely enclosed by, mendipite, and are usually also accompanied by malachite, cerussite and 'hydrocerussite', and occasionally by mimetite and/or wulfenite. Other oxychloride minerals such as mereheadite Pb 47 O 24 (OH) 13 Cl 25 (BO 3 ) 2 (CO 3 ) (Krivovichev et al, 2009), parkinsonite Pb 7 MoO 9 Cl 2 (Welch and Lepore, 2010), symesite Pb 10 (SO 4 )O 7 Cl 4 .…”

Section: Introductionmentioning

confidence: 99%

Yeomanite, Pb₂O(OH)Cl, a new chain-structured Pb oxychloride from Merehead Quarry, Somerset, England

Turner¹,

Siidra

Rumsey

et al. 2015

Self Cite

Yeomanite, Pb2O(OH)Cl, is a new Pb-oxychloride found in the manganese pod mineral assemblage at Merehead (Torr Works) Quarry, near Cranmore, Somerset, England. Yeomanite is named in joint recognition of Mrs Angela Yeoman (1931–) and her company, Foster Yeoman, who operated Merehead Quarry for aggregate until 2006. The mineral is normally white, occasionally grey, with a white streak and a vitreous to transparent lustre. Invariably intimately associated with mendipite, yeomanite appears to be formed of small, twisted, rope-like fibres growing from the end of columnar mendipite masses, forming loose mats and strands resembling asbestos. Individual fibres are generally <8 mm long, but exceptionally may reach up to 15 mm. There is a perfect cleavage parallel to the long axis of the fibres but this is masked by the fibrous nature, especially as individual fibres break easily. The Dcalc for the ideal formula is 7.303 g/cm3. The mean RI in air at 589 nm is 2.27. The eight strongest reflections in the powder X-ray diffraction pattern [(d in Å) (Intensity) (hkl)] are: 2.880(100)(113); 2.802(78)(006); 3.293(61)(200); 3.770(32)(011); 2.166(22)(206); 1.662(19)(119); 2.050(18)(303); 3.054(17)(105) Yeomanite is orthorhombic, Pnma, a = 6.585(10), b = 3.855(6), c = 17.26(1) Å, V = 438(1) Å3, Z = 4. Yeomanite is a new example of the growing family of lead oxychloride minerals that have a structure based upon oxocentred OPb4 tetrahedra, which, in this mineral, jointly with OHPb3 triangles, form [O(OH)Pb2]+ chains similar to those observed in synthetic Pb2O(OH)I. Yeomanite is structurally related to sidpietersite, penfieldite and laurionite.

“…The quarry is worked for aggregate; it is well known to geologists and mineral collectors for its unusual lead oxychloride mineral assemblage (Symes and Embrey, 1977;Turner and Rumsey, 2010). The mineralization in the quarry and surrounding area is of considerable scientific importance as it includes the type localities for the rare minerals mendipite (Spencer, 1923), chloroxiphite (Spencer, 1923;Siidra et al, 2008b), diaboleite (Spencer, 1923), parkinsonite (Symes et al, 1994), mereheadite (Welch et al, 1998;Krivovichev et al, 2009) and symesite (Welch et al, 2000).…”

Section: Occurrencementioning

confidence: 99%

“…6a). The [O 2 Pb 3 ] 2+ chains are similar to 43.127(12) Pb(8)ÀO(2) 2.42(5) Pb(1)ÀCl 13.438(10) Pb(1)ÀCl 13.438(10) Pb(9)ÀOH(3) 2.65(5) Pb(9)ÀOH 32.65(5) Pb(2)ÀO 22.24(5) Pb(9)ÀOH(5) 2.71(5) Pb(2)ÀO 22.24(5) Pb(9)ÀOH(5) 2.71(5) Pb(2)ÀOH 62.87(8) Pb(9)ÀCl(2) 2.883(16) Pb(2)ÀOH 62.87(8) Pb(9)ÀCl(2) 2.883(16) Pb(2)ÀCl 33.150(10) Pb(2)ÀCl 23.422(8) Pb(10)ÀOH(5) 1.99(6) Pb(2)ÀCl 23.422(8) Pb(10)ÀOH(5) 1.99(6) Pb(10)ÀOH 62.57(9) Pb(3)ÀO 12.23(4) Pb(10)ÀOH(6) 2.57(9) Pb(3)ÀO 12.23(4) Pb(10)ÀOH(6) 2.57(9) Pb(3)ÀOH 12.38(5) Pb(10)ÀOH(6) 2.57(9) Pb(3)ÀCl 33.354(12) Pb(10)ÀCl(2) 3.17(2) Pb(10)ÀCl 23.17(2) Pb(4)ÀO 12.44(3) Pb 4 (Krivovichev and Burns, 2001a;Siidra et al, 2008a), chloroxiphite [Pb 3 O 2 ]CuCl 2 (OH) 2 (Siidra et al, 2008b), and damaraite Pb 3 O 2 (OH)Cl (Krivovichev and Burns, 2001a 4. The coordination of Pb 2+ cations in the structure of rickturnerite.…”

Section: Chemical Compositionmentioning

confidence: 99%

Rickturnerite, Pb₇O₄[Mg(OH)₄](OH)Cl₃, a complex new lead oxychloride mineral

Rumsey¹,

Krivovichev²,

Siidra³

et al. 2012

Self Cite

Rickturnerite, which has the ideal formula Pb7O4[Mg(OH)4](OH)Cl3, is a new mineral from Torr Works (Merehead) quarry, near the village of Cranmore in Somerset, United Kingdom. It occurs as pale emerald green to grey porous aggregates of disordered interwoven minute fibrous crystals with mereheadite, cerussite, calcite, aragonite, mimetite, hydrocerussite, “plumbonacrite” and an uncharacterized lead oxychloride, in cavities inside a manganite and pyrolusite pod. The crystals are typically less than 5 μm wide and 200 μm long, but they can reach 40 × 100 μm in cross-section and over 1 mm in length. The mineral is translucent with a vitreous lustre and each needle is brittle with an indistinct cleavage, breaking with a splintery fracture. The streak is white, the Mohs hardness ∼3 and the density calculated using the empirical formula 6.886 g cm–3. Electron microprobe analyses yielded PbO 87.7, MgO 1.79, CuO 0.14, Cl 6.62 wt.%; H2O was calculated on the basis of structural considerations as 2.27 wt.% totalling 97.02 wt.%. A charge-balanced formula, based on 12 anions, is Pb7.16Mg0.81Cu0.03Cl3.40H4.60O8.60. Rickturnerite is orthorhombic Pnma, with a = 5.8024(6), b = 22.717(2), c = 25.879(3) Å, V = 3411.2(6) Å3 and Z = 8. The diffraction pattern contains strong reflections that define a subcell with a = 5.8034(5), b = 11.3574(9), c = 12.939(2) Å, V = 852.9(6) Å3 (space group Pmm2 which is related to the real unit cell by the transformation matrix [100/020/002]), and weak reflections that correspond to doubled b and c parameters. Since the difference between the large and small cells is only in a number of split and low-occupancy positions in the disordered region of the structure we provide the description of the subcell structure. The five strongest lines in the X-ray powder diffraction pattern [listed as dobs (Å), Iobs, (hkl)] are as follows: 6.474, 100, (400); 3.233, 73, (107); 2.867, 57, (705); 5.636, 44, (011); 3.112, 31, (802). The crystal structure was solved by direct methods and refined using 1318 unique reflections to R1 = 0.063. The structure is composed of a fully ordered part consisting of double [O2Pb3]2+ chains of oxocentred [OPb4] tetrahedra extended along the b-axis, which together with Cl– ions form 2-dimensional blocks parallel to (001). In between these blocks, there is a disordered region containing ordered [Mg(OH)6]4– octahedra and low-occupancy Pb and OH sites with a slight degree of ordering; these produce the weak supercell reflections.