Leifite

Leifite is a trigonal mineral, class 3 2/m, space group P3m1.[8] There are 3 formula units in the unit cell (Z = 3), and cell dimensions are 14.4 Å in the a direction and 4.9 Å in the c direction.[6][9] It contains OH groups, but no water of crystallization as was previously assumed.[10] Tetrahedrons of silicon or aluminium atoms surrounded by four oxygen atoms link to form six-membered rings stacked along the c direction to form channels, similar to those in zeolites.[8]

Leifite is generally white or colourless, with a white streak and a silky or vitreous lustre. It occurs as fine needles making up radiating aggregates and rosettes. Individual crystals are deeply striated hexagonal prisms that are transparent to translucent.[10]

The mineral is hard, with Mohs hardness 6, the same as that of feldspar, and specific gravity 2.6,[10] again like the feldspars. It is brittle, with an uneven to splintery fracture.[5][1]

Leifite is uniaxial(+)[10] with refractive indices n_ω = 1.516 and n_ε = 1.520.[6] The maximum birefringence δ = 0. 011.[5] Leifite is not luminescent.[4]

The type locality is the Narsaarsuk pegmatite on the Narsaarsuk Plateau, Igaliku, Narsaq, Kujalleq, Greenland[5] and type material is kept at the University of Copenhagen, Denmark, and at the National Museum of Natural History in Washington DC, US.[1] Leifite occurs in cavities in alkali-pegmatite veins.[3] At Mont Saint-Hilaire it occurs as crystals up to 5 cm long and as disk-shaped aggregates and radially fibrous spheres associated with albite, natrolite, serandite and catapleite.[7] In Greenland it occurs in a pegmatite with microcline, calcite, zinnwaldite and acmite.[7] In Russia it occurs in the Lovozero Massif associated with albite and natrolite.[1] In Norway it occurs in a nepheline syenite pegmatite on the south eastern part of the island of Vesle Aroya in the Langesundsfjord District, Oslo Region, as white to colourless fibrous masses and radiating bundles.[10]