Publication Type:Journal Article
Source:Mineralogical Magazine, Mineralogical Society, Volume 68, Number 4, p.615-632 (2004)
Keywords:Chlorite minerals, crystals, Drop breakup, Intermetallics, Platinum alloys, Twinning
Skaergaardite, PdCu, is a new mineral discovered in the Skaergaard intrusion, Kangerdlugssuaq area, East Greenland. It occurs in a tholeitiic gabbro associated with plagioclase, clinopyroxene, orthopyroxene, ilmenite, titanian magnetite, fayalite and accessory chlorite-group minerals, ferrosaponite, a member of the annite-phlogopite series, hornblende, actinolite, epidote, calcite, ankerite, apatite and baddeleyite. The mineral is found in composite microglobules composed of bornite, chalcocite, digenite, chalcopyrite, with rare cobalt pentlandite, cobaltoan pentlandite, sphalerite, keithconnite, vasilite, zvyagintsevite, (Cu,Pd,Au) and Pt-Fe-Cu-Pd alloys, unnamed PdCU3, (Pd,Cu,Sn), AU3Cu and PdAuCu. Skaergaardite occurs as droplets, equant grains with rounded outlines, subhedral to euhedral crystals and as irregular grains that vary in size from 2 to 75 m, averaging 22 m. It is steel grey with a bronze tint, has a black streak, a metallic lustre and is sectile. Neither cleavage nor fracture was observed. The mineral has a micro-indentation hardness of VHN25 = 257. It is isotropic, non-pleochroic and exhibits neither discernible internal reflections nor evidence of twinning. Skaergaardite varies from bright creamy white (associated with bornite and chalcopyrite) to bright white (associated with digenite and chalcocite). Reflectance values in air (and in oil) are: 58.65 (47.4) at 470 nm, 62.6 (51.1) at 546 mn, 64.1 (52.8) at 589 mn and 65.25 (53.95) at 650 nm. The average of 311 electron-microprobe analyses gives: Pd 58.94, Pt 1.12, Au 2.23, Cu 29.84, Fe 3.85, Zn 1.46, Sn 1.08, Te 0.28 and Ph 0.39, total 99.19 wt.%, corresponding to (Pd 0.967Au0.020Pt0.010 0.997(Cu0 .820Fe0.120 Zn0.039Sn0.16Te0.004Pb0.003 1 .002. The mineral is cubic, space group Pm3m, a = 3.0014(2) A, V = 27.0378 A3, Z = 1. D calc is 10.64 g/cm3 . The six strongest lines in the X-ray powder-diffraction pattern (d in A(I)(hkl)] are: 2.122(100)(110), 1.5000(20)(200), 1.2254(50)(211), 0.9491(20)(310), 0.8666(10)(222), 0.8021(70)(321). The mineral has the CsCl-type structure. It is believed to be isostructural with wairauite (CoFe), synthetic CuZn (-brass) and is structurally related to hongshiite (PtCu). Skaergaardite developed from a disordered Pd-Cu-rich metal alloy melt that bad exsolved from an earlier Cu-(Fe) sulphide melt. Ordering of Pd and Cu (beginning at T 600C) results in development of the CsCl structure from a disordered face-centred cubic structure. 2004 The Mineralogical Society.
Compilation and indexing terms, Copyright 2018 Elsevier Inc.<br/>2004498693342<br/>Chlorite-group minerals<br/>Skaergaardite<br/>Vasilite