POTASSICPARGASITE, A NEW MEMBER OF THE AMPHIBOLE GROUP FROM PARGAS, TURKU-PORI, FINLAND

Potassicpargasite, ideally (K,Na)Ca-2(Mg,Fe,Al)(5)(Si,Al)(8)O-22(OH,F) (2), is a new member of the amphibole group, presumed to be from Parga s, Turku-Pori, Finland. The holotype specimen is a 3 x 3 x 5 cm aggreg ate of randomly intergrown vitreous black prismatic crystals displayin g the dominant forms {110}, {011} and {010}, associated with minor pal e yellow calcite. It has a brownish green streak and is nonfluorescent in ultraviolet light. The mineral is brittle, with an uneven to conch oidal fracture, perfect {110} cleavage, and no observed parting. Its M ohs hardness is 6 to 6 1/2, D(meas.) 3.25(1) g/cm(3), D(calc.) 3.25 g/ cm(3) for the observed empirical formula and Z = 2. Optically, potassi cpargasite is biaxial negative, with alpha 1.654(1), beta 1.664(1), ga mma 1.670(1), 2V(meas.) 101(1)degrees, 2V(calc.) 105 degrees, X boolea n AND alpha 40 degrees (beta obtuse) and Y = b; absorption Z > Y > X, pleochroism Z dark olive green, Y olive green and X pale gray-green. T he mineral is monoclinic, space group C2/m, with refined unit-cell par ameters a 9.9199(4), b 18.0591(8), c 5.3180(3) Angstrom, beta 105.36(1 )degrees, V918.65(5) Angstrom(3), Z = 2, a:b:c 0.5493:1.0:0.2945. The seven strongest lines in the X-ray powder-diffraction pattern [d in An gstrom (I) (hkl)] are 3.140 (100)(<(3)over bar 10>), 8.451 (95)(110), 2.344 (70)(<(4)over bar 21>), 3.283 (45)(<(2)over bar 40>), 1.652 (40) (461). 2.707 (35)(151) and 2.018 (35)(351). Combined electron-micropro be, wet chemical, crystal structure, Mossbauer and combustion - IR ana lyses gave SiO2 41.63, TiO2 0.87, Al2O3 13.13, Fe2O3 2.20, FeO 11.00, MgO 11.86, MnO 0.16, CaO 12.33, K2O 2.83, Na2O 1.55, H2O 0.90, F 1.78, O = F -0.75, total 99.49 wt.%, corresponding to 0.253+Ti0.10Mn0.02)Si gma(5.00)(Si6.26Al1.74)(Sigma 8.00)O-22[(OH)(0.90)F0.85O0.25](Sigma 2. 00) on the basis of 24 anions. The structure, which is that of a clino amphibole, was refined to an R of 3.6%. The name is that provided by t he current IMA nomenclature for amphiboles.