Mattheddleite, a new mineral of the apatite group from Leadhills, Strathclyde Region

Abstract

Synopsis Mattheddleite, a new lead member of the apatite group with sulphur and silicon totally replacing phosphorus, occurs as tiny crystals (<0.1 mm) forming drusy cavities in specimens from Leadhills. Optically, the mineral is colourless in transmitted light and is uniaxial with ω2.017 and ε1.999. X-ray powder diffraction data are similar to the synthetic compound lead hydroxyapatite and may be indexed on a hexagonal cell with a 9.963 and c 7.464 Å (the cell volume is 642 Å 3 ). The calculated density is 6.96 g/cm 3 . The strongest lines in the powder pattern are [ d , ( I ) ( hkl )]: 2.988 (100) (112, 211), 4.32 (40) (200), 4.13 (40) (111), 2.877 (40) (300), 3.26 (30) (210). Single crystal Weissenberg photographs are close to those of pyromorphite, space group P6 3 /m. Chemically, mattheddleite does not contain S and Si in the expected 1:1 ratio, and the ideal formula may be expressed as Pb 20 (SiO 4 ) 7 (SO 4 ) 4 Cl 4 . The infrared spectrum is very similar to that of hydroxyellestadite. Associated minerals are lanarkite, cerussite, hydrocerussite, caledonite, leadhillite, susannite, and macphersonite. The mineral is named after Matthew Forster Heddle (1828–1897), a famous Scottish mineralogist.

Crystal structure of mattheddleite: a Pb, S, Si phase with the apatite structure

“…The standards were: natural PbS for Pb and S, synthetic anorthite glass for Si, and synthetic crystalline Ca 5 P 3 O 12 Cl for Cl. The results given in Table 1 basically agree with the results of Livingstone et al (1987) that atomic Si is not equal to S but rather has an average ratio of 1 S for 2.12 Si atoms for this Leadhills sample. This differs slightly from the value given in Livingstone et al (1987) (column 1, Table 1) for a sample from another location.…”

“…The results given in Table 1 basically agree with the results of Livingstone et al (1987) that atomic Si is not equal to S but rather has an average ratio of 1 S for 2.12 Si atoms for this Leadhills sample. This differs slightly from the value given in Livingstone et al (1987) (column 1, Table 1) for a sample from another location. Other elements including Mg, Al, P, Ca, Mn, As and V were sought but none was detected.…”

“…Calcium apatites with Si and S are included in the ellestadite group of minerals and it has been shown that Si and S substitute in near equal atom amounts for P to maintain charge balance (Si 4+ + S 6+ > 2P 5+ ) (Rouse and Dunn, 1982). In their description of mattheddleite, Livingstone et al (1987) pointed out that: (1) mattheddleite does not contain P; (2) S does not equal Si on an atomic basis; and (3) Si + S is not suf cient to ll the tetrahedral site. In fact, their sample from Leadhills, Scotland showed a S:Si ratio of 1:1.675 instead of the expected 1:1 for charge balance in the apatite structure.…”

Chlorellestadite, Ca5(SiO4)1.5(SO4)1.5Cl, a new ellestadite- group mineral from the Shadil-Khokh volcano, South Ossetia

“…5) is analogous to other spectra of the ellestadite group minerals (Harada et al 1971;Livingstone et al 1987;Onac et al 2006). The main bands correspond to the Si-O and S-O vibrations in tetrahedral sites.…”

Queitite, a mineral new to Britain, from the Caldbeck Fells, Cumbria

“…The composition of queitite bears comparison with that of mattheddleite, Pb20(5iO4)7(504)4C14 (Livingstone et al, 1987), which has also been found at Red Gill mine (Cooper et al, 1988), and their formation is likely to require rather similar conditions.…”