IMA 2017-096 = pampaloite

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Marco E. Ciriotti
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IMA 2017-096 = pampaloite

Messaggio da Marco E. Ciriotti » gio 05 lug, 2018 10:16

Prossima pubblicazione.

▪ Vymazalová, A., Kojonen, K., Laufek, F., Johanson, B., Stanley, C.J., Plášil, J., Halodová, P. (2018): Pampaloite, AuSbTe, a new mineral from Pampalo gold mine, Finland. Mineralogical Magazine, 82, (in press).

Pampaloite, AuSbTe is a new mineral discovered in the Pampalo gold deposit, Finland. It forms anhedral grains (up to about 20 μm) intergrown with gold, frohbergite and altaite. Pampaloite is brittle and has a metallic lustre. Values of VHN25 lie between 245 and 295 kg/mm2, with a mean value of 276 kg/mm2, corresponding to a Mohs hardness of approximately 4-5 (measured on synthetic material). In plane-polarized light, pampaloite is white with medium to strong bireflectance, weak reflectance pleochroism from slightly pinkish-brown to slightly bluish white (only visible in grains of synthetic material containing multiple orientations), and strong anisotropy, with blue to light brown rotation tints; it exhibits no internal reflections. Reflectance values of pampaloite in air (R1, R2 in %) are: 60.0, 62.5 at 470 nm, 62.5, 64.8 at 546 nm, 63.2, 65.6 at 589 nm and 63.7, 66.0 at 650 nm. Ten electron-microprobe analyses of natural pampaloite give an average composition: Au 44.13, Sb 27.44, and Te 28.74, total 100.31 wt.%, corresponding to the empirical formula Au1.00Sb1.00Te1.00 based on 3 atoms; the average of eleven analyses on synthetic pampaloite is: Au 44.03, Sb 27.26, and Te 29.08, total 100.38 wt.%, corresponding to Au0.99Sb1.00Te1.01. The density, calculated on the basis of the empirical formula, is 9.33 g/cm3.The mineral is monoclinic, space group C2/c, with a 11.947(3), b 4.481(1) Å, c 12.335(3) Å, β 105.83(2)º, V 635.3(3) Å3 and Z = 8. The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic AuSbTe. Pampaloite crystal structure can be considered as a monoclinic derivative of the CdI2-structure composed of [AuTe3Sb3] octahedra. The strongest lines in the X-ray powder diffraction pattern of synthetic pampaloite [d in Å (I) (hkl)] are: 4.846(24)(-202), 3.825(18)(111), 2.978(100)(-311), 2.968(50)(004), 2.242(25)(020), 2.144(55)(313), 2.063(33)(-315), 1.789(18)(024). The mineral is named for the locality, the Pampalo gold mine in Finland.
Marco E. Ciriotti

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