Odintsovite from the Ilimaussaq alkaline complex, South Greenland

The very rare mineral odintsovite has been found, for the first time outsid e of its type locality, at Mt. Nakalaq (Nakkaalaaq) in the Ilimaussaq alkal ine complex, South Greenland. The Ilimaussaq odintsovite occurs in microcli ne veins and is associated with, among other species a large number of Be-m inerals including bavenite, bertrandite, epididymite, genthelvite, helvite and leucophanite. At Mt. Nakalaq (Nakkaalaaq) the odintsovite forms flat, f an- to wheel-shaped aggregates up to 1 mm in diameter of 0.001 min thick, t an coloured crystals, directly in the microcline matrix. Odintsovite from I limaussaq is biaxial positive with 2V = 80 degrees, n(alpha)=1.6330, n(beta ) = 1.6455, n(gamma) = 1.664((calc)) white light, alpha = a, beta = b and g amma = c. The unit cell parameters of the odintsovite from Ilimaussaq, obta ined from powder diffraction data, are: a = 14.39(1), b = 12.85(1), and c = 33.86(4) Angstrom. Both the optical data and the unit cell parameters corr espond with those given for odintsovite from the type locality. The empiric al formula of the odintsovite from Ilimaussaq, calculated from the micropro be analyses is: K2.03Li.92(Na2.85Ca1.23)Sigma Ca-4.08(2)(Ti1.24Fe3+ Nb-.40(.39))(Sigma2.03) Be-4 (Si11.88Al.04) O-Sigma 11.92(38).