Abstract
Huemulite, a new mineral with the formula Na4MgV10O28 · 24H2O, was found in several uraniferous ore-bodies of the “sandstone-type deposits”, in the southwestern part of Mendoza province, Argentina. Huemulite appears in botryoidal masses, thin films, or as interstitial filling in the sandstone that is the host rock. It is soft, yellowish orange to orange in color, with a dull luster and specific gravity of 2.39 g/cm3. It is not fluorescent.
The mineral is easily soluble in cold water, giving an orange solution of pH 5.5 to 6.5. From this solution the mineral recrystallizes giving tabular crystals elongated parallel to (010), with a perfect cleavage parallel to (001) and less perfect parallel to (010). The optical properties determined in the recrystallized material show that the mineral is biaxial negative, 2V=25°–30°, pleochroic with X light yellow, Y golden yellow, and Z yellowish orange. The indices of refraction measured with sodium light are α=1.679, β=1.734, and γ=1.742. The dispersion is strong with r>v.
Chemical analyses were performed on both natural and recrystallized material. A synthetic compound was prepared which gives a x-ray powder, and single crystal data similar to those of huemulite.
Huemulite is triclinic, space group P1 or P1. Unit cell data obtained on the recrystallized material are: a=11.770 ű.019, b=11.838±.008, c=9.018±.009 Å, α=107°13′±05′, β=112° 10′±06′, γ=101° 30′±05′; a:b:c = 0.9943:1:0.7618. V=1040.67 Å3±2.70. Cell contents Na4MgV10O28 · 24H2O gives a calculated density of 2.40 g/cm3. The strongest lines of the x-ray powder diffraction pattern are: 7.6 (100), 10.6 (90), 9.1 (60), 10.2 (55), 8.2 (35), 3.05 (30), 5.26 (25).
The name huemulite comes from the Huemul mine, the most important uranium deposit of the area where the mineral was discovered.
