Jarlite (G = 3.87) is monoclinic, tabular on (001); space-group C2/m, C2, or Cm; a = 15.99, b = 10.82, c = 7.24 kX, β = 101° 49'; Y=b, Z: c = + (84° ± 2°); α = 1.430, β = 1.435, γ = 1.437, 2V=90° ± 10°; the composition NaSr3Al3F16 is apparently in error. “Metajarlite” (G = 3.65, with inclusions), with α= 1.429, β = 1.431, γ = 1.434, and an x-ray powder pattern very like that of jarlite, is merely a variety of jarlite. Prosopite is monoclinic, C2/c; a =6.67, b = 11.17, c 7.37 kX, β = 94° 56'. Weberite is orthorhombic, Ibmm or Ibml2; the unit cell with a = 7.30, b = 7.05, c 9.97 kX, contains 4[Na2MgAlF7]; X=a, Y = b. Cryo-lithionite has a = 12.14 kX. Powder photographs of ralstonite show indications of non-cubic symmetry, and “hagemannite” is an ochre consisting of ralstonite with some thomsenolite and goethite. X-ray powder spacings and intensities (10 scale) are given for gearksutite and ralstonite, and similar data with indices and calculated spacings are given for cryolite, jarlite and “metajarlite,” prosopite, and weberite. All the material studied, except prosopite from Colorado, came from Ivigtut, Greenland.

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