The composition, physical properties and occurrence of eucryptite from the Haapaluoma pegmatite, Finland.

Abstract

Eucryptite was found as nodules and aggregates = or <10 cm in diameter from the Haapaluoma lithium pegmatite in Peraseinajoki, western Finland. The mineral occurs as a rare accessory in postmagmatic fracture fillings and replacement bodies associated with quartz, cleavelandite and lithium silicates (elbaite, lepidolite and spodumene). Chemical analysis gave SiO2 51.74, Al2O3 36.76, Li2O 9.70, Fe2O3tot 0.99, CaO 0.30, Na2O 0.26, K2O 0.16, H2O+ 1.02, H2O- 0.12, = 100.06 (101.05). Electron microprobe analysis, however, indicates SiO2 47.5% and Al2O3 39.4% corresponding closely with the theoretical formula (LiAlSiO4). X-ray studies gave a 13.473, c 9.000 A, space group R3; the indexed X-ray powder pattern is given; sp.gr. 2.657; omega 1.585, epsilon 1.572. Some of the eucryptite specimens are polysynthetically twinned.-J.M.H.