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Mineralogical ClassificationRickturnerite / IMA 2010-034

16th Nov 2010 17:29 UTCRick Turner

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

17th Nov 2010 07:03 UTCMarco E. Ciriotti Manager

Best compliments, Rick.

Interesting phase!

17th Nov 2010 10:06 UTCSteve Rust Manager

Con grats on the new species Rick

22nd Nov 2010 02:15 UTCRobert Meyer Manager

Congratulations, Rick!

27th Jan 2012 11:58 UTCChris Stanley Expert

Now published:

M. S. Rumsey, S. V. Krivovichev, O. I. Siidra, C. A. Kirk, C. J. Stanley and J. Spratt (2012): Rickturnerite, Pb7O4(OH)Cl3, a complex new lead oxychloride mineral. Mineralogical Magazine 76, 59-73.

Rickturnerite, which has the ideal formula Pb7O4(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 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 2+ chains of oxocentred 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 4_ octahedra and low-occupancy Pb

and OH sites with a slight degree of ordering; these produce the weak supercell reflections.

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