Abstract

Ferri-clinoholmquistite is a new amphibole species from episyenites in the East Pedriza Massif (Central System, Spain), where it is associated to albite, augite-aegirine, titanite, andradite, magnetite, and apatite. It is black, vitreous, translucent, non-fluorescent, and brittle. It shows gray streak, H(Mohs) = 6, splintery fracture, perfect {110} cleavage, (001) parting, D meas = 3.19, and D cal = 3.25. Crystals are prismatic, elongated on [001]. In plane-polarized light, it is strongly pleochroic: X = yellow green, Y = indigo blue, Z = green blue, with absorption X<Y< or =Z; Z = b, Y - c = 10(2) degrees , X - a approximately -2 degrees (in beta obtuse). Ferri-clinoholmquistite is biaxial positive, alpha = 1.699(2), beta = 1.703(2), gamma = 1.708(2), 2V Z (meas) = 72(7), 2V Z (calc) = 84(6), r<v. It is monoclinic, space group C2/m, a = 9.472(4), b = 17.844(6), c = 5.276(6) Aa, beta = 101.97(9) degrees , V = 872(1) Aa 3 , Z = 2. X-ray powder-diffraction pattern data were determined. Analysis by a combination of electron microprobe and flame photometry gives the following formula, calculated assuming OH+F = 2 and T sites fully occupied by Si: A (Na (sub 0.43) K (sub 0.03) ) B (Li (sub 1.66) Na (sub 0.30) Ca (sub 0.04) ) C (Fe (super 3+) (sub 1.54) Fe (super 2+) (sub 1.35) Mg (sub 1.21) Li (sub 0.49) Al (sub 0.20) Ti (super 4+) (sub 0.12) Mn (super 2+) (sub 0.07) Zn (sub 0.02) ) T (Si 8 )O 22 (OH (sub 1.58) F (sub 0.42) ). From crystallographic refinements the M4 site is split, implying ordering of Li and Na, and within the A cavity, Na occupies the Am position.

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