MINERALOGICAL MAGAZINE, JUNE 1984, VOL. 48, PP. 277-82

Macphersonite, a new mineral from , Scotland, and Saint-Prix, France- a polymorph of and

A. LIVINGSTONE Department of Geology, Royal Scottish Museum, Chambers Street, Edinburgh EHI 1 JF, Scotland

AND

H. SARP

Departement de mineralogie et de petrographie, Museum D'Histoire Naturelle, Case Postale 284, Gent\ve 6, Switzerland

ABSTRACT. is white, resinous to mineral or synthetic inorganic analogue, and adamantine, hardness (Mohs) 21-3, density 6.50-6.55 further work revealed the mineral to be a new gm/cm3 and possesses a perfect on {OlD}. polymorph of leadhillite and susannite. Optically it is negative with 2V. 35-36°, (J.= 1.87, fJ = Subsequently, a submission to the IMA resulted y c, and y 2.00 and = 2.01, (J.= b, fJ = = a, in the new species, and name, being approved. r > v. Polysynthetic twinning, with either coarse or fine During the closing stages of the voting period a lamellae, is common, as are contact twins. Crystals are orthorhombic, tabular on b with a 10.37, b 23.10 and c second submission for an identical phase from the 9.25 A, cell volume 2215.8 A3 and Pcab;Z is 8 Argentolle Mine, near Saint-Prix, Saone-et-Loire, formula units. The seven strongest lines in the X-ray France, reached the IMA. Consequently, both powder pattern are 3.274 (50) 052; 3.234 (100) 251; 2.654 authors considered a joint publication to be in the (90) 351, 203; 2.598 (30) 172,400; 2.310 (30) 004, 371, 0.10.0; best interests of . With regard to the 2.182 (30) 263; and 2.033 (30) 234, 452, 154, 1.10.2. Saint-Prix material this was collected, as leadhillite, Electronprobe-microanalysis-determined chemistry at the Mine by Jean-Louis Passaqui, from Dijon, to the empirical formula (Pb4.08,Cuo 1 Cdo.07)~4.25So.90 0' and arrived at the Geneva Museum in the care of C2.18010.5S(OH)1.58 which yields the ideal formula Pb4(S04)(C03)z(OH)2 and hence macphersonite is a Eric Asselborn, a mineral collector. polymorph of leadhillite and susannite. The infrared The mineral is named after Dr Harry Gordon spectrum shows basic similarities to leadhillite and susan- Macpherson, Keeper of Minerals at the Royal nite spectra with additional diagnostic absorption bands. Scottish Museum, Edinburgh, Scotland. Macphersonite shows an identical thermogravimetric Physical and optical properties. Macphersonite behaviour to that ofleadhillite. It is associated, in varying from Leadhills is very pale amber en masse though combinations, with leadhillite, susannite, , cale- colourless in thin flakes whereas that from the donite, , , , and the ' Argentolle mine is colourless to white. The is hydroxyapatite' of Temple (1955). The new mineral adamantine on fresh surfaces otherwise resinous, mimics leadhillite. uneven, and Mohs hardness 21-3. Dilute hydrochloric and nitric acids are dissolvents that WITHIN the Heddle collection, at the Royal generate effervescence and a complete rapid dis- Scottish Museum, a small quartz specimen (ap- solution; in the latter acid, a curdy white PbS04 proximately 2 x 4 x 5 cm) from Leadhills Dod, precipitate forms. Using a Berman balance on a Leadhills, Lanarkshire, Scotland, bore the label 29.15 mg Leadhills fragment a density of 6.55 'Leadhillite? ?' In order to resolve the gmjcm3 resulted whereas the measured Argentolle dilemma an X-ray powder photograph of the macphersonite density is 6.50 gmjcm3. Densities mineral in question, which in colour and morpho- calculated from empirical formulae are 6.65 and logy neither resembles leadhillite nor anglesite, 6.60 gmjcm3 respectively. Cleavage is perfect on became essential. The resulting powder photo- {OlO}and the mineral is tabular on b. A very strong, graph could not be matched with that of any known vivid yellow fluorescence under long and short @ Copyright the Mineralogical Society 278 A. LIVINGSTONE AND H. SARP wave ultraviolet is displayed by Leadhills macpher- logies of a cleavage fragment (Leadhills) and an sonite although this fluorescence is characteristic of Argentolle crystal are shown in fig. 2, together with several Leadhills minerals. The Argentolle mac- the optic orientation. phersonite does not fluoresce. Very slight morpho- Detailed optical examination suggests ortho- logical differences exist between the two types for rhombic symmetry with a 2 V. of 35-36° and hence the rare Leadhills macphersonite (fig. 1) is a 'com- optically negative. Due to reactivity with high posite crystal' (2 x 3 x 7 mm) displaying interpene- liquids the optical constants for the trant growth which contrasts with the abundant Argentolle macphersonite are calculated values. In pseudo hexagonal, tabular to micaceous crystals this case ex(1.87) is derived from the axial angle and (2-5 mm) from the Argentolle Mine. The morpho- both fJ (1.98) and y (2.00) are calculated from reflectivity measurements made on- orientated polished sections. These values are in very good agreement with those actually determined for Leadhills macphersonite where ex= 1.87, fJ = 2.00, and y = 2.01. Optic orientation is ex= b, fJ = c, and y = a. Moderate dispersion was observed for Leadhills macphersonite with r > v and thus being opposite to strong leadhillite dispersion. In keeping with leadhillite, twinning is common in macphersonite also. Leadhills macphersonite displays lamellar twins with both broad and fine lamellae, the composition plane being parallel to {I02}. Twinned crystals of Argentolle macpherson- ite may attain I cm; contact twins (see fig. 2) are common and lamellar twins uncommon. X-ray crystallography. X-ray powder diffraction data for both types are detailed in Table I. An FIG. 1. Dumb-bell shaped composite crystal (2 x 3 x 114.6 mm diameter asymmetric Straumanis camera 7 mm) of macphersonite projecting from cavity, showing was used for Leadhills macphersonite and Guinier- interpenetrant growth. The cleavage runs parallel to the Hiigg and Gandolfi cameras for the Argentolle crystal length. Leadhills. mineral. The powder data in Table I are indexed on

1. 2. 3. FIG. 2. (1) Cleavage fragment of macphersonite, Leadhills. (2) Crystal drawing from a perfect crystal, and optic orientation of macphersonite. Argentolle Mine. (3) Pseudohexagonal contact twins. Argentolle Mine.

p = lines showing preferred orientation. Data obtained from 114.6 mm diameter camera, Cu-KD!, Ni filter. * t Data obtained from Guinier-Hiigg and Gandolfi; cameras, Cu-KD!, Ni filter. the basis of a 10.37, b 23.10, and c 9.25 A (cell pendicular to the perfect cleavage of all three volume 2215.8A3) obtained from a perfect Argen- polymorphs Argentolle b (23.10 A) is twice lead hill- toile crystal using precession X-ray photographs. ite and susannite c values of 11.56 and 11.54 A The Argentolle parameters demonstrate a relation- respectively. The Argentolle a parameter is exactly ship to those derived by Mrose and Christian (1969) half leadhillite b. Precession and de long photo- for leadhillite and susannite. In the direction per- graphs on Argentolle material, for Okl, hOIand hkO MACPHERSONITE, A NEW MINERAL 281 show the following extinction conditions; hkl no evolution profiles were very similar to those of condition, Okl I = 2n, hkO k = 2n, hOI h = 2n, hOO leadhillite (Morgan, pers. comm.), i.e. simultaneous h = 2n, 0011 = 2n and OkOk = 2n. These conditions evolution of HzO and approximately half the C02 lead to the space group Pcab. Both leadhillite and at 300°C in a well-defined, sharp reaction, followed susannite have Z = 8 formula units in the , by gradual release of the remaining COz. The as does macphersonite. thermogravimetric trace (0.94 mg sample) revealed Chemistry and thermal analysis. Leadhills mac- an initial sharp, weight loss between 250-320 DC phersonite analyses were undertaken using a followed by a slower loss up to 520°C. This agrees Cambridge Instruments Geoscan V utilizing with the evolved gas analysis results and is identical galena, copper and cadmium metals as standards. thermo gravimetric behaviour to that of leadhillite. Results for ten separate cleavage fragments (single Infrared spectra. Mrose and Christian (1969) in spot analysis per fragment) are given in Table II their abstract of unpublished data concluded that together with those for H20+ and C02 deter- leadhillite and susannite could be differentiated by mined on a 2.16 mg sample using thermogravi- their infrared spectra; this is confirmed for leadhill- metric and evolved gas analysis. The empirical ite and susannite from the Leadhills- Wanlockhead formula, calculated on the basis of 12 atoms area. Macphersonite produces an infrared spec- from the average analysis, is (Pb4.o8,CUO.10, trum which displays the basic similarities to the CdO.07h4.2SS0.90C2.18010.ss(OH)1.58' which leads above minerals although additional, sharp absorp- to the ideal formula Pb4(S04)(C03)2(OH)2' This tions are present which serve to distinguish it formula is identical to that of leadhillite and from the dimorphs. The Leadhills and Saint-Prix susannite and both these minerals were analysed macphersonite samples produce identical spectra. for comparative purposes using the same instru- Detailed infrared data for the three polymorphs ment and standards. All three polymorphs yielded a will form the subject of a separate note (see p. 295). consistent and identical composition although no Assemblage. The two assemblages in which traces of Cu and Cd were detected in leadhillite or macphersonite occurs are virtually identical. The susannite. Empirically, sulphur is slightly lower and Leadhills mineral is associated with leadhillite, C02 slightly higher than the ideal values. Low susannite, cerussite, , yellow pyromor- sulphur cannot be attributed to wavelength shift phite, and a milky-white mineral which produced due to valency differences between standard and an X-ray powder pattern akin to 'lead-hydroxy- unknown for the optimum 28 value for S (due to apatite' of Temple (1955). Argentolle associates are S04) was ascertained before measurement on the susannite, cerussite, pyromorphite, galena, quartz, unknown commenced. and scotlandite. Argentolle macphersonite conforms to the above The above common assemblages and abundance chemistry for analysis on approximately 2 gm using of leadhillite, combined with the macphersonite gravimetric and thermo gravimetric techniques physical characteristics, strongly suggest the yielded PbO 83.59, S03 7.65, C02 8.47, H20+ 1.93 mineral may masquerade as leadhillite. It is surpris- (total 101.64 %) which corresponds to Pb4.o6S1.03 ing that the polymorph has not been described CZ.OSOlO.1S(OHh.3Z' previously. Accordingly, leadhillite and macpher- Leadhills macphersonite COz and HzO+ sonite may mimic each other and a fairly rigorous

TABLE I I. Chemical composition of macphersonite from Leadhills Dod, Leadhills, Lanarkshire, Scotland

2 3 4 5 6 7 8 9 10 Ave.

PbO 84.4 84.1 82.9 84.2 83.5 83.5 83.4 82.2 83.6 82.0 83.4 SO, 6.4 6.9 6.4 6.4 6.4 6.5 6.5 6.7 6.7 6.7 6.6 CuO 0.06 0.08 0.06 0.05 0.05 0.01 0.08 0.13 0.12 0.15 0.1 CdO 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.0 0.1 CO2 8.8 H2O+ 1.3 Total 100.3

Anals. 1-10 electron probe microanalyses (single spot analysis per grain) of macphersonite (Royal Scottish Museum specimen number 721.34). Ave. Average of anals. 1-10 and including C02 and H20+ determined by thermo gravimetric and evolved gas analysis. 282 A. LIVINGSTONE AND H. SARP test will now be essential in order to distinguish the Acknowledgements. One of the authors (A.L.) is greatly species with certainty. Apart from a larger 2V indebted to Dr J. D. Russell of the Macaulay Institute for in macphersonite, either an X-ray powder photo- Soil Research for the infrared investigations. Thanks are graph or an infrared spectrum will be required to also due to Dr D. J. Morgan ofthe Geochemical Division, identify either leadhillite or macphersonite in the Institute of Geological Sciences, for thermal studies. future. The picture is complicated further for all Preparation of fig. 2 by Mr P. 1. Davidson and polished material for electron probe-microanalysis by Mr R. 1. three polymorphs may occur on the same specimen Reekie, both of the Royal Scottish Museum, is gratefully and leadhillite and susannite produce the same acknowledged. X-ray powder diffraction pattern. Type material from Leadhills is lodged in REFERENCES the Royal Scottish Museum and registered under number 721.34, and Argentolle macphersonite is Mrose, M. E., and Christian, R. P. (1969) Abstract, Can. Mineral. 10, 141. registered under number 435/80 within the Depart- Temple, A. K. (1955) Trans. R. Soc. Edinb. 63, 85. ment of Mineralogy and Petrography, Museum of Natural History, Geneva. [Manuscript received 16 June 1983J

[Note added in proof. The full of leadhillite and macphersonite has been recently determined from single crystal X-ray diffraction studies (Smith and Vickers, 1984, in preparation) and studies on susannite are in progress.J