Canadian Rockhound: Lukechangite-(Ce)

Lukechangite-(Ce)
Abstracted by Malcolm Back

Lukechangite-(Ce), ideally Na₃Ce₂(CO₃)₄F, originally designated as UK103 has been approved as a new mineral by the Commision on New Minerals and Mineral Names, IMA. The type locality is the Poudrette quarry, Mont Saint-Hilaire, Quebec. It was named in honor of Luke L.Y. Chang (1934), University of Maryland, for his contributions to the study of carbonate minerals. The cotype specimen, now in the collection of the Canadian Museum of Nature, Ottawa, CMNMI 81535, was collected in 1995 by Steve and Janet Cares. At present lukechangite-(Ce) must be considered to be extremely rare as only a few milligrams are known to exist.

The specimens were collected from a large pegmatite dyke in the nepheline syenite intrusion. The associated minerals are microcline, analcime, sodalite, aegerine, serandite, eudialyte, catapleiite, fluorite, petersenite-(Ce), siderite, astrophyllite, and albite. Horvathite-(Y), UK96, and UK93 were found in a different section of the same pegmatite, and the assemblage is thought to be a late-stage pegmatite.

Lukechangite-(Ce) has two distinct habits: 1) tabular, 0.5 to 1.0 mm. and 2) short prismatiuc to barrel-shaped crystals, 0.5 to 1.0 mm. across. The forms include {0001}, {11(bar2)0} and {11(bar2)1} plus at least one more bipyramid. Striations parallel {0001} are due to oscillatory growth of the bipyramid. Lukechangite-(Ce) is colourless to pale beige with a white streak and vitreous lustre, somewhat pearly on {0001}. Hardness is ~4½ (Mohs scale), brittle with an uneven to conchoidal fracture and with perfect {0001} cleavage. It does not fluoresce. The calculated density is 4.02 g/cm³, and is soluble in 1:1 HCl with effervescence. Lukechangite-(Ce) is uniaxial negative, w = 1.728(3) and e = 1.542(1) (l = 589 nm). It is hexagonal, space group P6₃/mmc, a 5.0612(8), c 22.820(9) Å, V = 509(1) Å, and Z = 2.

Source:

Grice, J.D. and Chao, G.Y. 1997. Lukechangite-(Ce) a new rare-earth-fluorocarbonate mineral from Mont Saint-Hilaire, Québec. Amer. Min. 82:1255-1260.

This article may not be copied, distributed or reprinted in any form without the author's permission. To contact the author, please use the e-mail address provided. If you are unable to contact the author, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author, original source and the Canadian Rockhound, and include the website URL address of the Canadian Rockhound.