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

Synopsis Mattheddleite, a new lead member of the apatite group with sulphur and silicon totally replacing phosphorus, occurs as tiny crystals ( a 9.963 and c 7.464 A (the cell volume is 642 A 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.