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Rickturnerite / IMA 2010-034

Posted by Rick Turner  
Rickturnerite / IMA 2010-034
November 16, 2010 05:29PM
A number of people have asked me to post a couple of images of this mineral, so this post is to oblige.

The first image (008) shows a pyramidal group of fibrous pale green rickturnerite crystals about 1cm high, on pale yellow-orange mereheadite, and calcite. This specimen is now in the National Museum of Wales, in Cardiff.

The second image (004) shows an interesting 'feather-like' aggregate of rickturnerite fibres, from my own collection. The green colour in both images is due to a small % of Cu replacing Mg. The dark spines are therefore simply thicker fibres; the mineral is white when thin.

Regards to all,

Rick
Attachments:
open | download - rickturnerite 008.jpg (181.7 KB)
open | download - rickturnerite 004.jpg (151.9 KB)
avatar Re: Rickturnerite / IMA 2010-034
November 17, 2010 07:03AM
Best compliments, Rick.
Interesting phase!
Re: Rickturnerite / IMA 2010-034
November 17, 2010 10:06AM
    
Con grats on the new species Rick
avatar Re: Rickturnerite / IMA 2010-034
November 22, 2010 02:15AM
Congratulations, Rick!
Re: Rickturnerite / IMA 2010-034
January 27, 2012 11:58AM
    
Now published:
M. S. Rumsey, S. V. Krivovichev, O. I. Siidra, C. A. Kirk, C. J. Stanley and J. Spratt (2012): Rickturnerite, Pb7O4[Mg(OH)4](OH)Cl3, a complex new lead oxychloride mineral. Mineralogical Magazine 76, 59-73.

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 x 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) A ˚ , V = 3411.2(6) A ˚ 3 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) A ˚ , V = 852.9(6) A ˚ 3
(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 (A˚ ), 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.



Edited 1 time(s). Last edit at 02/13/2012 01:43PM by Uwe Kolitsch.
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