At Hurricane Mountain, Carroll County, New Hampshire, bodies of granitic pegmatite in riebeckite granite contain large (up to 10 cm long and 2 cm across) primary crystals of Li-bearing fluor-arfvedsonite in miarolitic cavities, grading to euhedral Li- and F-poor arfvedsonite. Fine-grained, fibrous, light blue-gray riebeckite occurs as a late-stage hydrothermal filling in the miarolitic cavities. The early, Li-rich, fluor-arfvedsonite has: a 9.836(5), b 17.997(7), c 5.316(4) Aa, beta 103.735(4) degrees , V 914.20(6) Aa 3 ; Z = 2, D (sub meas.) 3.34 g/cm 3 , D (sub calc.) 3.353 g/cm 3 ; biaxial (-), 2V (sub meas.) 44(1) degrees , 2V (sub calc.) 46 degrees ; alpha 1.681(2), beta 1.692(2), gamma 1.694(2), inclined dispersion, r>v; X / c-7 degrees , Y = b, Z / a+7 degrees ; X dark blue, Y lavender gray, Z pale yellowish brown; X>Y>Z; X is opaque at 0.03 mm thickness. A structural formula, on the basis of 24 (O, OH, F) atoms is: (Na (sub 0.86) K (sub 0.25) )Na 2 (Fe (super 2+) (sub 2.54) Fe (super 3+) (sub 1.485) Mn (sub 0.10) Zn (sub 0.02) Li (sub 0.49) Ti (sub 0.07) ) (Si (sub 7.71) Al (sub 0.07) )O 22 (F (sub 1.34) OH (sub 0.63) ). Arfvedsonite within the miarolitic cavities contains less Li and F than that of the earlier generation, and the still later riebeckite contains only 0.09 wt.% Li 2 O and 0.3 wt.% F. The Fe (super 3+) :Fe (super 2+) ratio of the early Li-bearing fluor-arfvedsonite and that of the euhedral arfvedsonite crystals within miarolitic cavities is 0.58. The late, fibrous, cavity-filling riebeckite has an Fe (super 3+) :Fe (super 2+) ratio of 0.99. The total iron content of the three amphiboles increases with continued crystallization. These amphiboles are products of peralkaline pegmatites locally derived from peralkaline granite.

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