Abstract
Burbankite and calkinsite, two new rare-earth-bearing carbonates, have been discovered in veins in the Bearpaw Mountains of Montana. Burbankite is an anhydrous carbonate with the general formula Q6(CO3)5, where Q represents Na, Ca, Sr, Ba, and rare earths. Calkinsite is a hydrous carbonate with the formula (RE)2(CO3)3·4H2O, where RE represents the summation of the rare earths. Burbankite is unlike any other carbonate, and calkinsite resembles lanthanite but has less water.
The physical properties of burbankite are: Hexagonal; color, grayish yellow; H, 3½; Sp. gr., 3.50; uniaxial (−); ω, 1.627; ϵ, 1.615; cleavage, prismatic. The physical properties of calkinsite are: Orthorhombic; color, pale yellow; H, 2½; Sp. gr., 3.28; habit, platy, (010); biaxial (-); 2V, 57.2°; α, 1.569; β, 1.657; γ, 1.686; cleavage, (0101, perfect, (101} distinct; parting (?), (001).
X-ray crystallographic data for burbankite: a0= 10.53 Å ± 0.05 Å, c0=6.47 Å ± 0.02 Å, space group P63/mmc or , number of formula units in the unit cell is 2. X-ray crystallographic data for calkinsite: a0 = 9.57 Å ± 0.02 ±, b0= 12.65 Å ± 0.08 Å, c0=8.94 Å ± 0.02 Å, space group P2i 22i or D23, number of formula units in the unit cell is 4; a:b:c = 0.757:1:0.707. Morphological crystallography for calkinsite: p0:q0:r0=0.934:0.707:1; forms c {001}, b {010}, a {100}, d {102}, q {122}, r {132}; twinning plane {101}; crystal class, probably P 2/m 2/m 2/m.
Burbankite occurs with intimately intergrown ancylite as irregular masses or veinlets younger than calcite, and as separate crystals in calcite, in hydrothermal deposits composed essentially of silicates, carbonates, and sulfides. Calkinsite is a late mineral associated with barite in vugs and associated with lanthanite, barite, and goethite in porous areas of weathered burbankite and ancylite.
The minerals are named after W. S. Burbank and F. C. Calkins, of the U. S. Geological Survey.
