Sorensenite, a new sodium-beryllium-tin-silicate from the Ilímaussaq intrusion, South Greenland

Abstract

The new mineral sorensenite (Na₄SnBe₂Si₆O₁₆(OH) ₄) occurs in groups of prisms attaining diameters of several centimetres. The mineral is transparent or semitransparent, colourless, brown or pink. The crystals are monoclinic, a₀ = 18.58, b₀ = 7.45 and C₀ = 12.05, β = 98°09'. Space group C⁶_2h – I 2/a, C⁴_s - Ia.

There are two distinct cleavages. The specific gravity is 2.9, the hardness 5-5.5. The mineral sometimes forms flat pseudohexagonal triplets with the normal to <011> in (100) as twin axes.

The mineral is biaxial negative, 2V_α ( = small to 75°, n_α ( = 1.576-1.579, n_β = 1.581- 1.585 and n_γ = 1.584 - 1.586. The chemical analysis (by M.E. Kazakova):

SiO₂ 49.73, SnO₂ 20.07, Nb₂O₅ 0.75, Fe₂O₃ 0.04, BeO 8.02, Na₂O 15.95, K₂O 0.34, H₂O 5.24; total 100.14 corresponds to the formula: Na₄SnBe₂Si₆O₁₆(OH)₄.

The mineral occurs in analcime-rich bodies in nepheline-sodalite-syenites of the llímaussaq massif, South Greenland. It is abundant in a few localities. Sorensenite is named after professor Henning Sørensen, Copenhagen, who directs the investigations in the Ilímaussaq region.