Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wang, L. Articles by Zhang, Y. Search for Related Content GeoRef GeoRef Citation

Carmichaelite, a new hydroxyl-bearing titanate from Garnet Ridge, Arizona

Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-1063, U.S.A.

Carmichaelite [MO_2–x(OH)_x, where M includes Ti, Cr, Fe, Mg, and Al] is a new hydrous titanate from Garnet Ridge, an ultramafic diatreme on the Colorado Plateau in Arizona. It is named in honor of Ian S.E. Carmichael, Professor of Geology at the University of California, Berkeley, in recognition of his many contributions to petrology, especially his studies of Fe-Ti oxides in volcanic rocks. The new mineral occurs as platy, cinnamon-brown inclusions in mantle-derived pyrope crystals, which also contain inclusions of rutile, srilankite, ilmenite, minerals of the crichtonite group, spinel, and olivine. Carmichaelite is commonly in contact with rutile and occasionally with srilankite. The average composition is TiO₂ = 62.16, Cr₂O₃ = 18.43, Al₂O₃ = 1.88, V₂O₃ = 0.87, Nb₂O₅ = 0.37, FeO = 7.61, MgO = 2.80, H₂O (calc) = 5.76, total 99.89 wt%, giving an empirical formula close to Ti_0.62Cr_0.19Fe_0.09Mg_0.06Al_0.03V_0.01O_1.5(OH)_0.5. A cation (non-H) to (O+OH) ratio of 1:2 was confirmed by microprobe analysis of oxygen, and the presence of the hydroxyl component was supported by IR data. Carmichaelite is monoclinic, space group P2₁/c, with a = 7.706(1), b = 4.5583(6), c = 20.187(3) Å, ß = 92.334(2)°, V = 708.5(3) ų, and Z = 22. The calculated density is 4.13 g/cm³. The strongest diffraction lines [d(I, h k l)] from a calculated powder pattern are 2.842 (100, 15), 3.773 (94, 013), 2.664 (70, 213), 1.688 (54, 22), 1.679 (44, 226), 1.661 (44, 28), and 1.648 (34, 1.1.11). The crystal structure, which has been determined from single-crystal X-ray diffraction data, consists of stacked chains of cation octahedra within layers of hexagonal closest-packed anions. The arrangement of cation octahedra within a single chain has the same basic structural unit of five edge-sharing octahedra found in olivine, the humite group, and leucophoenicite.

Carmichaelite is inferred to have co-precipitated with its pyrope host and other titanates in the presence of a fluid or melt phase (i.e., mantle metasomatism) at temperatures of 650–750 °C and pressures of 20–25 kbar. It contains the highest OH content reported for titanates of mantle origin and offers a potential storage site for water and high field strength elements in the upper mantle. The new mineral is probably stabilized by high pressure and the high concentration of Cr. Certain features of the carmichaelite structure raise the possibility of a similar high-pressure phase in the Si-AlO-H system.

This article has been cited by other articles:

				N. Dobelin, L. Z. Reznitsky, E. V. Sklyarov, T. Armbruster, and O. Medenbach Schreyerite, V2Ti3O9: New occurrence and crystal structure American Mineralogist, January 1, 2006; 91(1): 196 - 202. [Abstract] [Full Text] [PDF]

				G. D. Bromiley and N. Hilairet Hydrogen and minor element incorporation in synthetic rutile Mineralogical Magazine, June 1, 2005; 69(3): 345 - 358. [Abstract] [Full Text] [PDF]

				J. A. Mandarino NEW MINERALS Can Mineral, June 1, 2002; 40(3): 1001 - 1020. [Full Text] [PDF]

				R. F. Martin and W. H. Blackburn ENCYCLOPEDIA OF MINERAL NAMES: SECOND UPDATE Can Mineral, August 1, 2001; 39(4): 1199 - 1218. [Full Text] [PDF]