Abstract

Fluoro-sodic-ferropedrizite, ideally ANaBLi2C(

\(\mathrm{Fe}_{2}^{2+}\)
Al2Li)TSi8O22WF2, is a new mineral of the amphibole group from the Sutlug River, Tuva Republic, Russia. It occurs at the endogenic contact of a Li-pegmatite with country rocks near to a diabase dyke and formed by reaction of the pegmatitic melt with the country rock. Fluoro-sodic-ferropedrizite occurs as prismatic to acicular crystals, ranging in length from 0.1-3 cm and widths of up to 50 μm. Crystals occur in parallel to sub-parallel aggregates up to 5 mm across in a matrix of calcite and plagioclase feldspar. Crystals are pale bluish-grey with a greyish-white streak. Fluoro-sodic-ferropedrizite is brittle, has a Mohs hardness of ∼6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage, no observable parting, and has a calculated density of 3.116 g cm-3. In plane-polarized light, it is pleochroic, X = pale purple-grey, Y = light grey, Z = colourless; X ^ a = 71.2° (in β acute), Y ∥ b, Z ^ c = 83.4° (in β obtuse). Fluoro-sodic-ferropedrizite is biaxial positive, α = 1.642(1), β = 1.644(1), γ = 1.652(1); 2V(obs) = 68.0(3)°, 2V(calc) = 56.4°. Fluoro-sodic-ferropedrizite is monoclinic, space group C2/m, a = 9.3720(4) Å, b = 17.6312(8) Å, c = 5.2732(3) Å, β = 102.247(4)°, V = 851.5(2) Å3, Z = 2. The strongest ten X-ray diffraction lines in the powder pattern are (d in Å,(I),(hkl)): 8.146,(10),(110); 2.686,(9),(151); 3.008,(8),(310); 4.430,(7),(021); 2.485,(6),(
\({\bar{2}}\)
02); 3.383,(4),(131); 2.876,(3),(
\({\bar{1}}\)
51,
\({\bar{3}}\)
11); 2.199,(3),(
\({\bar{3}}\)
12); 4.030,(2),(111) and 3.795,(2),(
\({\bar{1}}\)
31). Analysis by a combination of electron microprobe and crystal-structure refinement gives SiO2 59.81, Al2O3 12.66, TiO2 0.09, FeO 10.32, MgO 5.56, MnO 0.73, ZnO 0.17, CaO 0.20, Na2O 2.81, Li2O 4.80, F 2.43, H2Ocalc 1.10, sum = 99.65 wt.%. The formula unit, calculated on the basis of 24(O,OH,F) is A(Na0.68)B(Li1.92Na0.05Ca0.03)C(
\(\mathrm{Fe}_{1.16}^{2+}\)
Mg1.10
\(\mathrm{Mn}_{0.08}^{2+}\)
Zn0.02Al1.97Ti0.01Li0.66)T(Si7.98Al0.02)O22W(F1.03OH0.97). Crystal-structure refinement shows Li to be completely ordered at the M(3) and M(4) sites. Fluoro-sodic-ferropedrizite, ideally ANaBLi2C(
\(\mathrm{Fe}_{2}^{2+}\)
Al2Li)TSi8O22WF2, is related to the theoretical end-member `sodic-pedrizite', ANaBLi2C(Mg2Al2Li)TSi8O22W(OH)2, by the substitutions CFe2+CMg and WF → W(OH).

You do not currently have access to this article.