The structures of two crystals of Li-bearing fluor-arfvedsonite (1) (K (sub 0.32) Na (sub 0.68) )Na 2 (Li (sub 0.48) Fe (super 2+) (sub 2.83) Mn (super 2+) (sub 0.10) Zn (sub 0.06) Fe (super 3+) (sub 1.46) Ti (sub 0.07) )(Si (sub 7.88) Al (sub 0.12) )O 22 [F (sub 1.15) (OH) (sub 0.85) ] and (2) (K (sub 0.25) Na (sub 0.75) )Na 2 (Li (sub 0.48) Fe (super 2+) (sub 2.84) Mn (super 2+) (sub 0.11) Zn (sub 0.05) Fe (super 3+) (sub 1.45) Ti (sub 0.07) )(Si (sub 7.89) Al (sub 0.11) )O 22 [(F (sub 1.35) (OH) (sub 0.65) ] from a granitic pegmatite, Hurricane Mountain, New Hampshire, have been refined to R indices of 1.5(1.6)% based on 1380(1387) reflections measured with MoKalpha X-radiation. The unit cell parameters are (1) a 9.838(4), b 17.991(6), c 5.315(2) Aa, beta 103.78(3) degrees , V 913.7 Aa 3 and (2) a 9.832(3), b 17.990(7), c 5.316(3) Aa, beta 103.79(3) degrees , V 913.2 Aa 3 . Site-scattering refinement shows Li to be completely ordered at the M(3) site in these crystals. The amphibole composition is intermediate between fluor-arfvedsonite and fluor-ferro-leakeite with a small component (approximately 10%) of fluor-ferro-ferri-nyboite. These amphibole crystals project into miarolitic cavities in a pegmatitic phase of a riebeckite granite. The early-crystallizing amphibole is close to fluor-ferro-leakeite in composition, but becomes progressively depleted in Li and F as crystals project out into miarolitic cavities; the final amphibole to crystallize is a fibrous Li-poor riebeckite. Li plays a significant role in late-stage fractionation involving the crystallization of alkali amphibole in peralkaline granitic environments.

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