Synthesis and crystal-structure refinement of synthetic fluor- pargasite

Fluor-ferro-leakeite is a new amphibole species from the Canada Pinabete pluton, Questa, New Mexico, U.S.A.; it occurs in association with quartz, alkali feldspar, acmite, ilmenite, and zircon. It forms as anhedral bluish black crystals elongated along c and up to 1 mm long. It is brittle, H = 6, Dmeas= 3.37 glcm3, Deale= 3.34 glcm3. In plane-polarized light, it is strongly pleochroic, X = very dark indigo blue, Y = gray blue, Z = yellow green; X /\ c = 10°(in (3obtuse), Y = b, Z /\ a = 4° (in (3obtuse), with absorption X > Y> Z. Fluor-ferro-leakeite is biaxial positive, a = 1.675(2), (3= 1.683(2), 'Y = 1.694(1); 2 V = 87(2)°; dispersion is not visible because of the strong absorption. Fluor-ferro-leakeite is monoclinic, space group C2/m, a = 9.792(1), b = 17.938(1), c = 5.3133(4) A, (3= 103.87(7)°, V = 906.0(1) A3, Z = 2. The ten strongest X-ray diffraction lines in the powder pattern are [d(I,hkl)]: 2.710(100,151),2.536(92):02),3.404(57,131), 4.481(54,040), 8.426(45,110), 2.985(38,"141),2.585(38,061), 3.122(29,310), 2.165(26,261), and 1.586(25,403). Analysis by a combination of electron microprobe, ion microprobe, and crystal-structure refinement (Hawthorne et al. 1993) gives Si02 51.12, Al203 1.13, n02 0.68, Fe203 16.73, FeO 8.87, MgO 2.02, MnO 4.51, ZnO 0.57, CaO 0.15, Na20 9.22, K20 1.19, Li20 0.99, F 2.87, H20calC0.60, sum 99.44 wt%. The formula unit, calculated on the basis of 23 0 atoms, is (Ko.23Nao.76)(Na1.97Cao.o3)(M&>.46FeI.t4Mnfi.!9Zllo.o7Fetk Tio.osAlo.o2Lio.6J(Si7.8lAlo.19)02iFu90HoA.61p)r'evious crystal-structure refinement (Hawthorne et al. 1993) shows Li to be completely ordered at the M3 site. Fluor-ferro-leakeite, ideally NaNa2(Fe~+Fe1+Li)Sis022F2,is related to leakeite, NaNa2(Mg2Fe~+Li)Sis022(OH)2, by the substitutions Fe2+-+ Mg and F -+ OH.