Hostname: page-component-586b7cd67f-g8jcs Total loading time: 0 Render date: 2024-11-29T13:55:46.606Z Has data issue: false hasContentIssue false
  • English
  • Français

Mineralogy of stalactites formed by subaerial weathering of natrocarbonatite hornitos at Oldoinyo Lengai, Tanzania

Published online by Cambridge University Press:  05 July 2018

R. H. Mitchell
R. H. Mitchell*
Affiliation:
Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, Canada P7B 5E1
*
*E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Stalactites formed by the chemical weathering of natrocarbonatite lava decorate the roofs of hollow inactive hornitos at Oldoinyo Lengai, Tanzania. The stalactites are composed principally of trona with lesser and very variable amounts of nahcolite, (NaHCO3), thermonatrite (Na2CO3.H2O), aphthitalite [(K,Na)3Na(SO4)2], kogarkoite [Na3(SO4)F], schairerite [Na21 (SO4)7F6Cl], halite and sylvite. Stalactites are considered to form by the evaporation of Ca-free highly alkaline brines seeping from the altered lavas which form the roofs of the hornitos. The principal subaerial weathering products of natrocarbonatite, i.e. pirsonnite, gaylussite, shortite and calcite are not found in the stalactites and are retained in the altered lavas of the homito roof. Fluorine required for the formation of kogarkoite and schairerite is derived from the decomposition of fluorite at high pH (>10). Sulphur is derived from the decomposition of gregoryite.

Keywords

natrocarbonatiteOldoinyo Lengaistalactitesmineralogy
Type
Editorial
Information
Mineralogical Magazine , Volume 70 , Issue 4 , August 2006 , pp. 437 - 444
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2006

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Church, A. A. and Jones, A. P. (1995) Silicate-carbonatite immiscibility at Oldoinyo Lengai. Journal of Petrology, 36, 869–889.CrossRefGoogle Scholar
Dawson, J. B. (1989) Sodium carbonatite extrusions from Oldoinyo Lengai, Tanzania: implications for carbonatite complex genesis. Pp. 255–277 in: Carbonatites: Genesis and Evolution (Bell, K., editor). Unwin Hyman, London.Google Scholar
Dawson, J. B. (1993) A supposed sovite from Oldoinyo Lengai: a result of extreme alteration of alkali carbonatite lava. Mineralogical Magazine, 57, 93–101.CrossRefGoogle Scholar
Dawson, J. B., Garson, M. S. and Roberts, B. (1987) Altered former alkalic carbonatite lava from Oldoinyo Lengai, Tanzania: inferences for calcite carbonatite lavas. Geology, 15, 765–768.2.0.CO;2>CrossRefGoogle Scholar
Dawson, J. B., Pinkerton, H., Norton, G. E., Pyle, D. M., Browning, P., Jackson, D. and Fallick, A. E. (1995) Petrology and geochemistry of Oldoinyo Lengai lavas extruded in November 1988: magma source, ascent and crystallization. Pp. 47–69 in: Carbonatite Volcanism (Bell, K. and Keller, J., editors). Springer-Verlag, Berlin.CrossRefGoogle Scholar
Dawson, J. B., Pyle, D. M. and Pinkerton, H. (1996) Evolution of natrocarbonatite from a wollastonite nephelinite parent: evidence from the June 1993 eruption of Oldoinyo Lengai, Tanzania. Journal of Geology, 104, 41–54.CrossRefGoogle Scholar
Fanfani, L., Nunzi, A., Zanazzi, P. F., Zanazri, A. R. and Sabelli, C. (1975) The crystal structure of schairerite and its relationship to sulphohalite. Mineralogical Magazine, 40, 131–139.CrossRefGoogle Scholar
Fanfani, L., Giuseppetti, G., Tadini, C. and Zanazzi, P. F. (1980) The crystal structure of kogarkoite Na3SO4F. Mineralogical Magazine, 43, 753–759.CrossRefGoogle Scholar
Foote, H. W. and Schairer, J. F. (1930a) The system Na2SO4-NaF-NaCl-H2O. I. The ternary systems with water and two salts. Journal of the American Chemical Society, 52, 4202–4209.CrossRefGoogle Scholar
Foote, H. W. and Schairer, J. F. (1930b) The system Na2SO4-NaF-NaCl-H2O. II. The quaternary system at 25 and 35°. Journal of the American Chemical Society, 52, 4210–4217.CrossRefGoogle Scholar
Genge, M. J., Balme, M. And Jones, A. P. (2001) Salt-bearing fumarole deposits in the summit crater of Oldoinyo Lengai, northern Tanzania: interaction between natrocarbonatite lava and meteoric water. Journal of Volcanology and Geothermal Research, 106, 111–122.CrossRefGoogle Scholar
Giguère, A. and Campbell, P. G. C. (2004) Fluoride toxicity towards freshwater organisms and hardness effects – new review and reanalysis of existing data. Revue Science Eau, 17, 373–393.CrossRefGoogle Scholar
Harvie, C. E., Moller, N. and Weare, J. (1984) The prediction of mineral solubilities in natural waters: the Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O system to high ionic strengths at 25°C. Geochimica et Cosmochimica Acta, 48, 723–751.CrossRefGoogle Scholar
Keller, J. and Krafft, M. (1990) Effusive natrocarbona¬tite activity at Oldoinyo Lengai, June 1988. Bulletin Volcanologie, 52, 629–645.CrossRefGoogle Scholar
Krauskopf, K. B. (1979) Introduction to Geochemistry. McGraw-Hill Book Company, New York.Google Scholar
Marion, G. M. (2001) Carbonate mineral solubility at low temperatures in the Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O system. Geochimica et Cosmochimica Acta, 65, 1883–1896.CrossRefGoogle Scholar
McFarlane, D. A., Lundberg, J. And Belton, F. (2004) An unusual lava cave from Oldoinyo Lengai, Tanzania. Journal of Cave and Karst Studies, 66, 98–101.Google Scholar
Mitchell, R. H. (1997) Carbonate-carbonate immiscibil¬ity, neighborite and potassium iron sulphide in Oldoinyo Lengai natrocarbonatite. Mineralogical Magazine, 61, 779–789.CrossRefGoogle Scholar
Mitchell, R. H. (2006) Sylvite and fluorite microcrysts and fluorite-nyerereite intergrowths from natrocar-bonatite, Oldoinyo Lengai, Tanzania. Mineralogical Magazine, 70, 103–114.CrossRefGoogle Scholar
Mitchell, R. H. and Belton, F. (2004) Nioealite-euspidine solid solution and manganoan monticellite from natrocarbonatite, Oldoinyo Lengai, Tanzania. Mineralogical Magazine, 68, 787–799.CrossRefGoogle Scholar
Moore, J. G. and Nicholas, G. (1964) Speleology - The Study of Caves. D.C. Heath, Boston, USA.Google Scholar
Outokumpu HSC Chemistry (2002) Outokumpu HSC Chemistry for Windows v. 5.0. Outokumpu Research Oy, Pori, Finland.Google Scholar
Pabst, A. and Sharp, W. N. (1973) Kogarkoite, a new natural phase in the system Na2SO4-NaF-NaCl. American Mineralogist, 58, 116–127.Google Scholar
Pabst, A., Sawyer, D. L. and Switzer, G. (1963) Galeite and related phases in the system Na2SO4-NaF-NaCl. American Mineralogist, 48, 485–510.Google Scholar
Peterson, T. D. (1990) Petrology and genesis of natrocarbonatite. Contributions to Mineralogy and Petrology, 105, 143–155.CrossRefGoogle Scholar
Spencer, R. J. (2000) Sulphate minerals in evaporite deposits. Pp. 173–192 in: Sulfate Minerals (Alpers, C. N. Jambor, J. L. and Nordstrom, D. K., editors). Reviews in Mineralogy & Geochemistry, 40, Mineralogical Society of America and the Geochemical Society, Washington, D.C.Google Scholar
Zaitsev, A. N. and Keller, J. (2006) Mineralogical and chemical transformations of Oldoinyo Lengai natrocarbonatites, Tanzania. Lithos, in press.CrossRefGoogle Scholar